common/rc: add _scratch_{u}mount_idmapped() helpers

They will be used in follow-up patches for xfs quota tests but might be
useful for other tests in the future.

Cc: Eryu Guan <guan@eryu.me>
Cc: Christoph Hellwig <hch@lst.de>
Cc: David Howells <dhowells@redhat.com>
Cc: fstests@vger.kernel.org
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>
6 files changed