Fix the inject_metadata_into_fs in the disk API.
Fix the inject_metadata_into_fs in the disk API.

Updates the _inject_metadata_into_fs in the disk/api.py so
that it uses dict-style access. This resolves an issue introduced
in a recent no-db-messaging change.

Includes new test case.

Fixes LP Bug #1034040.

Change-Id: I1bc90a8331419709ab71e5da8c48cd1d54c40f9e

n0ano/ganttclient