ceph.spec: create /var/run on package install

The %ghost %dir ... line will make this get cleaned up but won't install
it.

Reported-by: Derek Yarnell <derek@umiacs.umd.edu>
Signed-off-by: Sage Weil <sage@inktank.com>
Reviewed-by: Gary Lowell <gary.lowell@inktank.com>