Refs #12911 - Fixing colon method calls

fixes #12730 - removing the fakeFS gem

fixes #7548 - cannot use UTF8 characters from ldap auth source

Fixes #7568 - Use attr_accessible for Rails 4 upgrade

Fixes #12325 - Add to_utf8 method and ensure avatar_path returns in utf-8

Fixes #7537 - Adds test connection button to LDAP form

Fixes #12059 - AuthSourceLdap allow_nil should be removed

When we migrated to the new migration syntax, the clause
`validate_length_of :host` was wrongly translated. It contains a clause
`allow_nil` that allows it to be nil, but in Rails 3 the `:presence =>...

Fixes #11407 - Uppercase logins from LDAP break external user group sync

On LDAP the login can contain uppercase chars, for instance, "FOO". However
when we log in Foreman for the first time and have that account auto-created,
we can login using "foo". After that, our login will be saved as "foo" on...

Fixes #11428 - External user groups refresh shouldn't be case sensitive

group_list in ldap_fluff returns a list of lowercase LDAP GIDs.
When AuthSourceLdap tries to run update_usergroups to refresh the external
user groups, it will try to match these lowercase gids with external user...

Fixes #10713 - improved backtrace logging

• full trace in 500 page in production shows really the full trace
• Foreman::Logging.exception as an unified entry point for exceptions logging
• the backtrace cleaner doesn't delete the plugins
• the orchestration exceptions gets the backtrace covered by logger...