Portability fix: mount.glusterfs

Remove bash-specific syntax from mount.glusterfs

This is a backport of  Iec3a52686f7cee1825ac5a06c11fb8ac4d3e5d65

BUG: 1138897
Change-Id: I3149cd4d94c862a3857709c00cf0ed0377976f40
Signed-off-by: Emmanuel Dreyfus <manu@netbsd.org>
Reviewed-on: http://review.gluster.org/9045
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Kaleb KEITHLEY <kkeithle@redhat.com>
Reviewed-by: Vijay Bellur <vbellur@redhat.com>