OpenSolaris/OpenIllumos: use /bin/bash if available for test scripts.

OpenSolaris/OpenIllumos: use /bin/bash if available for test scripts.

t_client.sh relies on "echo -e" and "echo -n" to produce nicely
looking output, which fails on Solaris /bin/sh - force SHELL=/bin/bash
on recent-enough Solaris variants that have it.

Signed-off-by: Gert Doering <gert@greenie.muc.de>
Acked-by: David Sommerseth <davids@openvpn.net>
Message-Id: <20191009120043.22692-1-gert@greenie.muc.de>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg18914.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>