Add oslo-config-1.2.0a2 and pbr>=0.5.16 to requirements.

See bug #1189889.

Change-Id: Id0dae9cea96ee779bc94a095d1ec5d046f2b39b4
Fixes: bug #1189889
Merge "Add oslo-config-1.2.0a2 and pbr>=0.5.16 to requirements."