don't count clusters as copies

don't count clusters as copies

Since the cluster UUID is inserted into the location log when the
location log lists a node as containing content.

Also avoid trying to lock content on cluster remotes. The cluster nodes
are also proxied, so that content can be locked on individual nodes, and
locking content on a cluster as a whole probably won't be implemented.

And made git-annex whereis use numcopies machinery for displaying its
count, so it won't count cluster UUIDs redundantly to nodes.
Other commands, like git-annex info that also display numcopies
information already used the numcopies machinery.

There is more to be done, fromNumCopies is sometimes used to get a
number that is compared with a list of UUIDs. And limitCopies doesn't
use numcopies machinery.