Start monit after bootstrapping

* Create symlink to start monitoring with runit if necessary

See complementary pull request: https://github.com/cloudfoundry/bosh/pull/706
it seems like there is no need to do this conditional since fs.Symlink is idempotent: https://github.com/cloudfoundry/bosh-agent/blob/master/system/os_file_system.go#L199