Gracefully handle Users with no email attribute

In certain environments, such as when using Keystone with a LDAP
backend, it's possible that the email attribute won't exist for all
users.

Change-Id: I71041be832206e52bfb73926199f2c89e0e84a0b
Closes-Bug: #1260423
Support warning messages in SelfHandlingForm

Sometimes we need to show a prominent message at the top of a form to
warn the user about something. One example is trying to snapshot an
in-use volume.

Change-Id: I073fe6bd049eb90b7a6ed45abfad96ebda3510eb
Related-Bug: #1202929
Merge "Gracefully handle Users with no email attribute"
Merge "Support warning messages in SelfHandlingForm"