tests: Allow tests to use customized command line parameters

Tests will now return the extra command line parameters they need
when run with --params

Signed-off-by: Bryce Harrington <bryce@osg.samsung.com>
Reviewed-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>

tests/weston-tests-env

@@ -46,5 +46,6 @@ case $TESTNAME in
 			--shell=$SHELL_PLUGIN \
 			--log="$SERVERLOG" \
 			--modules=$TEST_PLUGIN,$XWAYLAND_PLUGIN \
+			$($abs_builddir/$TESTNAME --params) \
 			&> "$OUTLOG"
 esac