api: glusterfs-api.pc.in (and libgfchangelog.pc.in) use rpath (-Wl,-R...)

Change-Id: Icdd23f1c31421c882db106cdad1b1406569594ca
BUG: 1002220
Signed-off-by: Kaleb S. KEITHLEY <kkeithle@redhat.com>
Reviewed-on: http://review.gluster.org/5717
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Anand Avati <avati@redhat.com>