Add a script to create review dashboard for a milestone

Add a script to create review dashboard for a milestone

This script queries launchpad to get:
1) Bug number of bugs tagged with rfe-approved
2) Bug number of critical/high bugs
3) list of blueprints targeted for the milestone passed as param

With this information the scripts prints queries that can be used
in Gerrit directly and creates a .dash file that can be used by
gerrit-dash-creator to output a dashboard url.

Change-Id: I09f8c04c6c609d4791bd5af825105ba092831e43