devmapper: exclude the root of a file tree walk
devmapper: exclude the root of a file tree walk

When we walk the directory of mount information, don't try to load
information from the root of the walk, which produces a confusing error
message.

Signed-off-by: Nalin Dahyabhai <f562fcb2a0b898bf0be1afc867ea92325d8f825f@redhat.com>

rhatdan/storage,containers/storage,containers/storage,rhatdan/storage,containers/storage,rhatdan/storage