Adding image location selection strategy

Under the design for this BP, those strategies are all be static and configured by Cloud owner/admin or operator.
In future, we can do a local metrics tracking library for client side, to get the dynamic performance metrics and save those indicators to local. Locality is critical because different glance nodes likely have different relationships to the underlying locations in terms of network distance, so each node should be gearing towards what is best for it.
--zhiyan

Addressed by: https://review.openstack.org/58263
    Adding image location selection strategies

Addressed by: https://review.openstack.org/58482
    Apply image location selection strategy

A near miss on icehouse-2, but with the gate going slow and only one patch ready to land, Iets just try to land this ASAP in icehouse 3. Still on top of my review queue! :-)

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Sample test sequence to play this feature. --zhiyan

1. Enable 'show_image_direct_url' option and/or 'show_multiple_locations' option for glance api service, for example:

$ cat /etc/glance/glance-api.conf | grep 'show_'
show_image_direct_url = True
show_multiple_locations = False

2. Set 'location_strategy' option to 'location_order' or 'store_type' for glance api service as you needed, like this:

$ cat /etc/glance/glance-api.conf | grep 'location_strategy'
location_strategy = location_order

Currently glance has only two built-in strategies, and if you choose to use 'store_type' as your image location selection strategy then you should configure 'store_type_preference' option within 'store_type_location_strategy' configuration group. For more details of the option please refer descriptions in glance.conf template.

3. Start/restart glance api service to apply those options.

4. Create an image for testing and get image id from response, for example:

$ curl -i -X POST -H 'X-Auth-Token: 7792c8f4500d4b2d9699135815840b26' -H 'Content-Type: application/json' -H 'User-Agent: python-glanceclient' -d '{"container_format": "bare", "disk_format": "qcow2", "name": "image_test", "visibility": "public"}' http://10.20.0.1:9292/v2/images

5. Assign multiple locations to the image via PATCH, like this:

$ curl -X PATCH -H 'X-Auth-Token: 7792c8f4500d4b2d9699135815840b26' -H 'User-Agent: python-lient' -H 'Content-Type: application/openstack-images-v2.1-json-patch' -i http://10.20.0.1:9292/v2/images/12d618d6-df2a-4e5d-8047-24d31883a1d1 -d '[{"op": "replace", "path": "/locations", "value": [{"url": "file:///home/lzy/image_test_loc_1", "metadata": {}}, {"url": "http://10.20.0.1:8000/image_test_loc_2", "metadata": {}}]}]'

{"status": "active", "name": "image_test", "tags": [], "container_format": "bare", "created_at": "2014-01-30T21:14:25Z", "size": 13147648, "disk_format": "qcow2", "updated_at": "2014-01-30T21:19:37Z", "visibility": "public", "self": "/v2/images/12d618d6-df2a-4e5d-8047-24d31883a1d1", "min_disk": 0, "protected": false, "id": "12d618d6-df2a-4e5d-8047-24d31883a1d1", "file": "/v2/images/12d618d6-df2a-4e5d-8047-24d31883a1d1/file", "owner": "4a0c4051e04a45a193e9bf1a9db3b923", "direct_url": "file:///home/lzy/image_test_loc_1", "min_ram": 0, "schema": "/v2/schemas/image"}

6. Verify image status under 'active' and end user can reach image direct locations as he configured selection strategy, for instance:

$ curl -i -X GET -H 'X-Auth-Token: b2817fe4c9d948ceafdf037b917e086b' -H 'Content-Type: application/json' -H 'User-Agent: python-glanceclient' http://10.20.0.1:9292/v2/images/12d618d6-df2a-4e5d-8047-24d31883a1d1

{"status": "active", "name": "image_test", "tags": [], "container_format": "bare", "created_at": "2014-01-30T21:14:25Z", "size": 13147648, "disk_format": "qcow2", "updated_at": "2014-01-30T21:19:37Z", "visibility": "public", "locations": [{"url": "file:///home/lzy/image_test_loc_1", "metadata": {}}, {"url": "http://10.20.0.1:8000/image_test_loc_2", "metadata": {}}], "self": "/v2/images/12d618d6-df2a-4e5d-8047-24d31883a1d1", "min_disk": 0, "protected": false, "id": "12d618d6-df2a-4e5d-8047-24d31883a1d1", "file": "/v2/images/12d618d6-df2a-4e5d-8047-24d31883a1d1/file", "owner": "4a0c4051e04a45a193e9bf1a9db3b923", "direct_url": "file:///home/lzy/image_test_loc_1", "min_ram": 0, "schema": "/v2/schemas/image"}

Note, in this case I'm using 'location_order' location selection strategy and enabled 'show_multiple_locations' option for show your details.
And now, from above result you can see the image loctions have been listed as its original order which I provided in above step (first one is 'loc_1' and second is 'loc_2') within 'locations' field, and as we expected the 'direct_url' give a correct value (the first one).

7. As alternative location strategy, if end user use ''store_type' strategy, and give 'http, file' as the value for 'store_type_preference' option, then the image locations result will as following:

{"status": "active", "name": "image_test", "tags": [], "container_format": "bare", "created_at": "2014-01-30T21:14:25Z", "size": 13147648, "disk_format": "qcow2", "updated_at": "2014-01-30T21:19:37Z", "visibility": "public", "locations": [{"url": "http://10.20.0.1:8000/image_test_loc_2", "metadata": {}}, {"url": "file:///home/lzy/image_test_loc_1", "metadata": {}}], "self": "/v2/images/12d618d6-df2a-4e5d-8047-24d31883a1d1", "min_disk": 0, "protected": false, "id": "12d618d6-df2a-4e5d-8047-24d31883a1d1", "file": "/v2/images/12d618d6-df2a-4e5d-8047-24d31883a1d1/file", "owner": "4a0c4051e04a45a193e9bf1a9db3b923", "direct_url": "http://10.20.0.1:8000/image_test_loc_2", "min_ram": 0, "schema": "/v2/schemas/image"}

In above result, the image locations have been exposed as 'store_type_preference' option requireed which we configured (first one is 'loc_2' and second is 'loc_1'), it's different then I initial provided of course.

End.