Update vmops to access metadata as dict.
Update vmops to access metadata as dict.

Updates the inject_instance_metadata in xenapi/vmops.py so
that it accesses metadata as a dict instead of an object.

This resolves issues causing exceptions when booting instances
on XenServer.

Fixes LP Bug #1033963

Change-Id: I58810764abd32d9d292f8282b54c126bf1f4de18

n0ano/ganttclient