Fix nested() for py3

nested() should return enter_context instead of
nothing.

Change-Id: I910eace453d07e2f9a12dd0ce0eca22f4d155472
Workflow documentation is now in infra-manual

Replace URLs for workflow documentation to appropriate parts of the
OpenStack Project Infrastructure Manual.

Change-Id: I318dea15e0d2f7ef22427fe22d8d57173e60e784
Updated from global requirements

Change-Id: I3443352b9ec847534cf4016dc540da769501593b
Merge "Fix nested() for py3"
Fix test_migrate_cli for py3

Use __lt__ insted of __cmp__ for py3 compatability.

Change-Id: I85d8eeb2cbb754b72b04c817f49d3a62f1473994
Merge "Fix test_migrate_cli for py3"