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>
tools: libcephfs-ize ceph-client-debug

Using the libcephfs calls but relying on client/ headers
to traverse the resulting data structures.

Signed-off-by: John Spray <john.spray@inktank.com>
tools: Use lookup-parent to get ino path

This avoids the need to modify the lookup_ino
response to include the (normally not needed)
parent dentry.

Signed-off-by: John Spray <john.spray@inktank.com>
fixup use lookup parent
client/libcephfs: Atomic lookup & ref inode

This is useful for clients that want to do something
(safely) with the inode object they've just retrieved.

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