common_fs_utils: use common method to extract id from role
common_fs_utils: use common method to extract id from role

This works with multiple clusters too.

Signed-off-by: Josh Durgin <1442af5e32b56bc0fa9c40ad9e4d67aeb05f1e26@redhat.com>

dmick/teuthology,dmick/teuthology,ceph/teuthology,ktdreyer/teuthology,ceph/teuthology,dmick/teuthology,SUSE/teuthology,SUSE/teuthology,ktdreyer/teuthology,SUSE/teuthology