add mistralclient to list of OSC plugins to test
add mistralclient to list of OSC plugins to test

mistralclient also uses openstackclient, so when checking for
duplicate and/or malformed commands, include mistralclient as well.

Change-Id: Id2cd618d276a131d94b04e6c76b13a38992fb943

noorul/os-project-config,dongwenjuan/project-config,Tesora/tesora-project-config,noorul/os-project-config,dongwenjuan/project-config,openstack-infra/project-config,Tesora/tesora-project-config,openstack-infra/project-config