build: sync glusterfs.spec.in with Fedora glusterfs.spec

 * add glusterfs-api and glusterfs-api-devel sub-packages
 * add extras/systemd/glusterd.service. Use it (or extras/init.d/glusterd)
   instead of the Fedora versions.
 * restores ability to build glusterfs RPMs from the dist tarball with
   'rpmbuild {-ts,-tb,-ta} glusterfs-XXX.tar.gz'
 * other minor cleanups mostly to sync with fedora .spec and to build
   from the dist tarball. Any differences will be resolved in the fedora
   .spec in the next release (i.e. beta4 or GA).

(still considering whether to add fedora glusterfsd.{init,service} files
to glusterfs or remove them from fedora.)

BUG: 950083
Change-Id: Ibda3cd57b24ef5c2a27446703e718e5044ec546c
Signed-off-by: Kaleb S. KEITHLEY <kkeithle@redhat.com>
Reviewed-on: http://review.gluster.org/5230
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Bala FA <barumuga@redhat.com>
Reviewed-by: Niels de Vos <ndevos@redhat.com>