Add unit tests for commands

This commit adds commands function.

Partially implements bp unit-tests

Change-Id: If5e037546965e338ebb9a171a178826b4e3136d6
Add keystone api version detection to verify_tempest_config

This commit adds a check for the keystone api versions that are
supported and checks that with the config file. In the process of
adding the additional check the version verification code is reworked
to use a common get versions method.

Partially implements bp config-verification

Change-Id: Ibb15c53e2b2a1e2a2ad95351692d06389f2ebb06
Merge "Add unit tests for commands"
Merge branch 'master' of https://github.com/openstack/tempest