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: I6fa85618c916a90fdbed5b231ea58bb51c9d2b70
BUG: 950083
Signed-off-by: Kaleb S. KEITHLEY <kkeithle@redhat.com>
Reviewed-on: http://review.gluster.org/6473
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Niels de Vos <ndevos@redhat.com>