Use /bin/bash instead of /bin/sh

It seems to be assuming that it is bash anyway

Change-Id: Ic3b5b579b45ab8836aa3b2db2c4332fe2f9ef62a
Reviewed-on: http://review.couchbase.org/30953
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>
Tested-by: Trond Norbye <trond.norbye@gmail.com>