Align UrlValidator to validate_url gem implementation 
Summary
Rename UrlValidator avoid 'url:' naming collision with ActiveModel::Validations::UrlValidator in 'validates' statement.
Make use of the options attribute of the parent class ActiveModel::EachValidator and add more options: regex.
Steps to reproduce
When adding the gem "openid-connect" to Gemfile, will pull the "validate_url" dependency that will overload the internal validator https://gitlab.com/gitlab-org/gitlab-ce/blob/master/app/validators/url_validator.rb with a different expectation for what a valid url means.
What is the current bug behavior?
When the new dependency is loaded the test for url will fail.
What is the expected correct behavior?
Introduce new dependencies and all spec tests should run as expected.