rgw: Allow wildcard in supported keystone roles.

http://tracker.ceph.com/issues/4365 fixes #4365

Signed-off-by: Christophe Courtaut <christophe.courtaut@gmail.com>
Merge pull request #562 from kri5/wip-4365

rgw: Allow wildcard in supported keystone roles.

Reviewed-by: Yehuda Sadeh <yehuda@inktank.com>