mds: Include parent dirent in lookup_ino response

It's not the full trace, but it's enough for a client to
follow the breadcrumbs back to the root.

Signed-off-by: John Spray <john.spray@inktank.com>
tools: ceph-client-debug

Signed-off-by: John Spray <john.spray@inktank.com>
tools: uniform json output in ceph-client-debug

So that a test script can easily parse the stdout
stream in one go.

Signed-off-by: John Spray <john.spray@inktank.com>