Re-raise exception using six

Using six.reraise() to re-raise an exception makes it compatible with
Python 2 and 3

Closes-Bug: 1351973
Change-Id: I11d1ce35794f2c6cfebafe5211ab8d880c4a826c
Rename add_error methods: Django 1.7 conflict

In Django 1.7, Forms have an add_error() method and our definition
was conflicting with Django's method. Thanks to hertzog@debian.org
for the patch.

Close-bug: #1352919
Change-Id: I1f558cf7f3198a68629738a011e9cae0c3749320
Automatically discover "Image Format" based on file extension

This commit can automatically pre-populate the "Format" field in
the "Create Image" modal after the user has filled out the "Image
Source" or "Image File" fields. This can be done based on the file
extension and save the user from filling out one additional field
in this modal.

Change-Id: Id6e3f3b3f8e354ce077a8f05f2bd5029b7fa9628
Closes-Bug: #1324192
Fix 'Associate' and 'Disassociate Monitor' actions

Since context['pool_monitors'] is not a list of monitors' ids anymore,
lists of possible monitors choices were broken. Now 'Associate Monitor'
and 'Disassociate Monitor' forms show proper health monitors lists for
associating/disaccociating.

Closes-Bug: #1351572
Change-Id: If496652ac082ad9fa2beba26bc7f6849ebf4cc14
Merge "Rename add_error methods: Django 1.7 conflict"
Merge "Automatically discover "Image Format" based on file extension"
Merge "Re-raise exception using six"
Merge "Fix 'Associate' and 'Disassociate Monitor' actions"