Due to http://tracker.ceph.com/issues/18309 the pid file for fuse clients
should always be set to the empty string. (Teuthology's default ceph.conf
sets it to /var/run/ceph/$cluster-$name.pid)
This commit adds a reusable yaml facet for this purpose.
Signed-off-by: Nathan Cutler <ncutler@suse.com>
