refs: Add argument --list to print the full ref name

Signed-off-by: Giuseppe Scrivano <gscrivan@redhat.com>

tests/test-refs.sh

@@ -45,6 +45,9 @@ assert_file_has_content refscount "^10$"
 ${CMD_PREFIX} ostree --repo=repo refs foo > refs
 assert_not_file_has_content refs foo
 
+${CMD_PREFIX} ostree --repo=repo refs --list foo > refs
+assert_file_has_content refs foo
+
 ${CMD_PREFIX} ostree --repo=repo refs foo | wc -l > refscount.foo
 assert_file_has_content refscount.foo "^5$"