The usage doc stated that plug and unplug accept a single argument of
type `os_vif.objects.VIF`, which isn't a thing, and then went on to give
an example showing that they take two. The usage doc and the plug and
unplug docstrings also listed various objects at the wrong paths (e.g.
the `instance_info` param being of type `os_vif.objects.InstanceInfo`,
which also isn't a thing).
Fixed up the usage doc to list both arguments and correct the references
in the sample code; and fixed the plug/unplug docstrings
to list the proper paths to classes: os_vif.objects.vif.VIFBase and
os_vif.objects.instance_info.InstanceInfo.
Made everything in `single backticks` into a proper rst ``literal``.
Change-Id: I400838bbe9663917fe2c64f52975b77a370405b4
8d7c0d548d