mds: Fix remotebit::dump for less common types

This was hitting an assertion when used on anything
other than a regular/symlink/dir.  Now covers
all types.

Signed-off-by: John Spray <john.spray@inktank.com>
Merge pull request #1480 from ceph/wip-remotebit-dump

mds: Fix remotebit::dump for less common types

Reviewed-by: Sage Weil <sage@inktank.com>