report port number for address already in use errors

* nova/wsgi.py(Service.__init__): Catch external errors
(socket.error is a subclass of EnvironmentError since python 2.6),
and log the port number attempted to bind to.

Closes-Bug: 1237961
Change-Id: Ia4eb46c76db855fc3168c5b7a233ce94d2ef7726
Merge "report port number for address already in use errors"