unregister runner

Accordingly the gitlab docs, it exists 3 commands to unregister a runner. The module use the command by name.

During unregister process, we got the following error message : Error: Evaluation Error: Error while evaluating a Function Call, assert_type(): expects a String value, got Undef at /.../gitlabrunner/manifests/init.pp:47:22

https://gitlab.adullact.net/adullact/puppet-gitlabrunner/blob/master/manifests/init.pp#L47

Be cause the method used is by name, $_runner_settings['registration-token'] and $_runner_settings['url'] must be used only during registration with $_runner_ensure present.

The unregister command must quote the description to able to handle description with space : https://gitlab.adullact.net/adullact/puppet-gitlabrunner/blob/master/manifests/unregister.pp#L12