change shell to bash to allow bash specific features (#4449)

Fixes: #3598
Change-Id: Ic5fd8ab840d179dbf163ffa97341c94f2bddf6eb

Signed-off-by: Pranith Kumar Karampuri <pranith.karampuri@phonepe.com>

Author: pranithk

extras/backend-cleanup.sh

@@ -1,4 +1,4 @@
-#!/bin/sh
+#!/bin/bash
 
 # This script can be used to cleanup the 'cluster/distribute' translator's 
 # stale link files. One may choose to run this only when number of subvolumes

tools/gfind_missing_files/gfind_missing_files.sh

@@ -1,4 +1,4 @@
-#!/bin/sh
+#!/bin/bash
 
 ##  Copyright (c) 2015 Red Hat, Inc. <http://www.redhat.com/>
 ##  This file is part of GlusterFS.

xlators/mount/fuse/utils/mount.glusterfs.in

@@ -1,4 +1,4 @@
-#!/bin/sh
+#!/bin/bash
 #
 # Copyright (c) 2013 Red Hat, Inc. <http://www.redhat.com>
 # Copyright (c) 2015 ungleich GmbH <http://www.ungleich.ch>