build: Merge glusterfs.spec changes from Fedora

sync with FedoraSCM glusterfs.spec

N.B. the %doc hack for clear_xattrs.sh doesn't work in the CentOS 5 mock
builds of the rpm.t regression test, thus I'm leaving that out for now

Change-Id: I3dce7ad2f850e7255b40b3fab0a2b0e44c724e83
BUG: 1039965
Signed-off-by: Kaleb S. KEITHLEY <kkeithle@redhat.com>
Reviewed-on: http://review.gluster.org/6474
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Niels de Vos <ndevos@redhat.com>