Update to controller-runtime 0.7.0

controller-runtime methods now accept `client.Object` and
`client.ObjectList` rather than `runtime.Object`. This means the
adapter interfaces need to change signature, but happily, little else.

Since the list adapter is now distinct to the object adapter, `len()`
can go there instead of the command-specific interfaces.

Signed-off-by: Michael Bridgen <michael@weave.works>