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>

configure.ac

@@ -306,6 +306,7 @@ case "$host" in
 		AC_DEFINE([TARGET_SOLARIS], [1], [Are we running on Solaris?])
 		AC_DEFINE_UNQUOTED([TARGET_PREFIX], ["S"], [Target prefix])
 		CPPFLAGS="$CPPFLAGS -D_XPG4_2"
+		test -x /bin/bash && SHELL="/bin/bash"
 		;;
 	*-*-openbsd*)
 		AC_DEFINE([TARGET_OPENBSD], [1], [Are we running on OpenBSD?])