check: don't abort on non-existent excluded groups

Don't abort the whole test run if we asked to exclude groups that aren't
included in the candidate group list, since we actually /are/ satisfying
the user's request.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>

check

@@ -243,7 +243,7 @@ _prepare_test_list()
 		list=$(get_group_list $xgroup)
 		if [ -z "$list" ]; then
 			echo "Group \"$xgroup\" is empty or not defined?"
-			exit 1
+			continue
 		fi
 
 		trim_test_list $list