Add logging to metadata parsing
Add logging to metadata parsing

The TaggedAttachmentsTest class queries server metadata to see if the
tagging is visible from the guest. However when the check fails it does
not log what was the faulty metadata. To make troubleshooting easier
this patch adds logging for the error cases.

Change-Id: I58f6fefef0f0a9db2f7fdf2a1a0125f616319949

openstack/tempest,openstack/tempest