scripts: Use `/bin/bash` not `/bin/sh`

If using `/bin/sh` this is what we see

$ ./who-wrote-glusterfs.sh
./who-wrote-glusterfs.sh: 39: shift: can't shift that many

Use `/bin/bash` instead where 'shift' without an argument
is supported.

Change-Id: I2be05f0062eb8456631c1cee859757052f1b6dc7
BUG: 1087771
Signed-off-by: Harshavardhana <harsha@harshavardhana.net>
Reviewed-on: http://review.gluster.org/7496
Reviewed-by: Niels de Vos <ndevos@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>