inspect should use the host from last inspection

[cornelius]

When inspect -n NAME is run on a description which already exists, the address of the inspected host should be taken from the description, so that a reinspection of a host becomes possible without having to provide the host address again.

So running machinery inspect 1.2.3.4 -n myhost when description myhost does not exist yet, would create the description. Running machinery inspect myhost when the description myhost already exists (created with the command from before) will effectively run machinery inspect 1.2.3.4 -n myhost again.