Rally & Tempest integration (base)

Use tempest (https://github.com/openstack/tempest) inside rally to organize base for verification functionality & for benchmarks scenario based on tempest.

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Tempest base
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We should implement couple of features inside rally:

new directory:
/verification - that will contains all stuff related to tempest

I think that best way is to have Verifier class that will contains all required method to work with tempest.

For start I think it will be enough to have:

outside of Verifier class
1) dictionally that contains {set_name: list_of_regexp_that_descirbes_set}

inside Verifier class:
1) run_set(set_name) # runs set of tests
2) run_tempest_test() # runs tempest tests
3) run # run all tempest tests

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Verification stuff
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1) Add CLI command that installs tempest
2) Add CLI command that makes git checkout <#hash_of_commit>, and precreated values like grizzly-1 grizzly-2 ..., havana-1, havana-2, ... , master
3) Add CLI command rally verify start (with 2 optional parameters --set <set_name> , --times <number>, --last (run what you run last time) and --last_failed (run last failed)

That's all