Quota error message should be more descriptive

forms.ValidationError will be raised if there are invalid quota values.
The error message would be like: Quota value cannot be less than the
current usage value: ram used: 512, instances used: 1.

Change-Id: I6734de7df6c146d647bbc89090d49a48e1b074ae
Closes-bug: 1274234
Add a None option to the CONSOLE_TYPE setting

We where able to set the CONSOLE_TYPE in local_settings.py, but not able to
deactivate it.

We added a new option to CONSOLE_TYPE which is None.
To keep the legacy behaviour, CONSOLE_TYPE defaults to 'AUTO' and has to be
explicitly set to None to deactivate the console.

implements bp hide-vnc-console-access

Change-Id: Id23f3d5e37509b846858d480ad781f2b4ffc3590
Merge "Add a None option to the CONSOLE_TYPE setting"
Merge branch 'master' of https://github.com/openstack/horizon