[ci] Don't install manila-tempest-plugin system-wide

System-wide installation via the tempest plugin's
devstack-plugin is unnecessary since we set the
"TEMPEST_PLUGINS" devstack localrc variable with
manila-tempest-plugin, and that should handle installing
the plugin alongside other tempest requirements within
a test virtual environment.

Change-Id: Id312005dc0cc9e039a9c6a8a58476965e8d6954d
Signed-off-by: Goutham Pacha Ravi <gouthampravi@gmail.com>
1 file changed