glusterfs.spec.in: sync with fedora glusterfs.spec

remove hard-coded reference to swift version and dist tarballs

minor improvements for rpm builds for regression tests, including
adding cache on build.gluster.org to avoid random failures due to
transient network or dns failures causing curl or git to fail.

BUG: 819130
Change-Id: I4f1213056ae2987dd2202f9cfbb3ed4f16ffc7cf
Signed-off-by: Kaleb S. KEITHLEY <kkeithle@redhat.com>
Reviewed-on: http://review.gluster.org/4674
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Justin Clift <jclift@redhat.com>
Tested-by: Justin Clift <jclift@redhat.com>
Reviewed-by: Anand Avati <avati@redhat.com>