The manila CLI was already deprecated in favor of the openstack CLI
plugin[1]. Install openstackclient when client is requested so that
the openstack CLI can be used.
[1] ba9a3887869ecd4cbed4aeb43c11a3d9493fafa2
Change-Id: I4589f6d74b3f4b6b88333306eb013b91fc0a9d44