Adjust shell scripts to allow Bash in other locations

Linux-based OS for the most part provide Bash and being located in /bin,
but on other OS's the shell would be in another location. Utilize env(1)
and allow it to be located elsewhere.

[ Reimplementation of upstream patch from Brad Smith <brad@comstyle.com>. ]

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: I99c2b4d0dbf6ab5e6f06a8d1fb0646aa69c639f5