Horizon needs to support filtered pages of users and projects, once it's supported by Keystone

Summary
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Horizon needs to support filtered pages of users and projects, once it's supported by Keystone v3 API to provide more user-friendly UI and avoid existing perfomance issues with fetching large datasets from services and rendering these datasets on one page without pagination.

Motivation
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1) Currently there is no way to paginate the table of Users fetched from LDAP behind Keystone. When there are a lot of users in LDAP, Keystone will response with timeout error, and when Keystone has a lot of users in mysql, rendering all these users without paging causes Horizon timeout.
2) Fetching a lots of users from Keystone causes Horizon slowness on every pages, where Horizon calls user_list or project_list.
3) Rendering of Identity/Users with more than 500 users takes too much time (more than 10 seconds)
4) It also causes slownes everywhere where Horizon uses api.keystone.user_list() call. For example, some workflows. And in some cases it cause errors (like that: https://bugs.launchpad.net/horizon/+bug/1504190)

Description
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First we need to get Keysone truncated flag support get merged. https://review.openstack.org/#/c/234849/
Next we need to get keystone-pythonclient truncated flag support to get merged
https://review.openstack.org/#/c/250473/1

UX
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When Horizon gets truncated dataset from Keystone, it should show notification in right top corner and ask user to specify his query with filtering.

Wireframes, Mocks, Videos and UI Markup
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N/A

Testing
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Should be covered both with unit and integration tests.

Outside Dependencies
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Keystone and python-keystoneclient supporting truncated flag for list() method

Requirements Update Required
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N/A

Doc Impact
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