Configurable network labels used for showing IPs in instance details

The ip shown in the instance detail was hard coded to be obtained from
a nova netwok label 'private' or 'usenet'. With this change, the labels
is configurable based on a regex pattern.

Fixes bug 1206303

Change-Id: I73d896e6b85bdebe342a777219b9b60d6954f8b6
Merge "Configurable network labels used for showing IPs in instance details"