This command allows us to uninstall a Tempest plugin.
E.g.
$ rally verify uninstallplugin --repo-name hello-world-tempest-plugin
Also, the patch has the following changes:
1. Now Tempest is installed in the local env (without deps) when providing
the --sistem-wide argument. It is needed to list plugins installed in the
local env, not in Tempest virtual env.
2. Now plugins are installed in the 'plugins/system-wide' directory when
providing the --system-wide argument. It is needed to separate plugins
installed in the local env and in Tempest virtual env.
Change-Id: Ic30a2705edb321a8d5af70e9d2bf5d5d5d9e8781
54ebdf4010