fixes #7253 - change nil admin field on users to false, matches usergroups

When the admin field was nil, admin_changed? in user model validations can
evaluate to true if the field changed from nil to false.
fixes #3105 - use untranslated string for PuppetCA state filter
fixes #4375: provisioning no longer loops when using oVirt + compute profile
Fixes #7139: Subnet name is limited to 255 chars