autoconf: Add fix for sh verses bash issues

Libtool scripts were finding bash was /bin/sh and then using bashisms which
then got into sstate and used on machines where /bin/sh might be dash.

This changes things to search for bash first since its preferred. We then hardcode
bash into the scripts which is more correct.

This does mean we have a dependency on bash but many of our scripts have
that anyway.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
Open-webOS-DCO-1.0-Signed-off-by: Martin Jansa <martin.jansa@lge.com>
Change-Id: I10c80b7bbaf2aa9efd0dff570095edbbfbf919d9
Reviewed-on: https://g2g.palm.com/3567
Reviewed-by: Susan Montooth <susan.montooth@lge.com>
Reviewed-by: Martin Jansa <Martin.Jansa@lge.com>
Tested-by: Martin Jansa <Martin.Jansa@lge.com>