support installing clients at released versions

expand the devstack support for libraries from released versions to
support python-* clients and tempest_lib.

Depends-On: I81b0d228e7769758c61e5b0323ecfce8c8886d39

Change-Id: I26fac0ccf8fd4818e24618d56bf04b32306f88f6
Merge "support installing clients at released versions"