Make the metadata paths use conductor

This patch makes the metadata service use conductor instead of hitting the
database directly.

It adds a get_ec2_ids() method to conductor, which encapsulates a bunch of
very small id translation database queries. It also does the AZ lookup
via conductor.

Fixes bug 1120402

Change-Id: Iceef753b1451ff53e29dfbf97a696b952b47d5a3
Merge "Make the metadata paths use conductor"