Documentation changes

Brought some of the calls in-line with the current thinking.
headnode_{connect,detach}_network

This is pretty much just copypasta from the node_ versions, and we
should abstract out what they have in common somehow.

I also snuck in a few small fixes:

1. Hnic's headnode_id column should be an integer, not a string
2. We should check that the nic label and node label "match" in
   detach_network.