Use bash for bin/background_scripts

The bin/background_jobs_sk_cluster script use some
bashisms. In order to avoid issues with either GDK
or other systems, here we make use of bash as the
default interpreter.

bin/background_jobs

-#!/bin/sh
+#!/bin/bash
 
 cd $(dirname $0)/..
 

bin/background_jobs_sk

-#!/bin/sh
+#!/bin/bash
 
 cd $(dirname $0)/..
 app_root=$(pwd)

bin/background_jobs_sk_cluster

-#!/bin/sh
+#!/bin/bash
 
 cd $(dirname $0)/..
 app_root=$(pwd)