Start monit after bootstrapping

* Create symlink to start monitoring with runit if necessary

See complementary pull request: https://github.com/cloudfoundry/bosh/pull/706
`sv start` is the same as `sv up` except with a 7 second delay (http://smarden.org/runit/sv.8.html) - this was necessary since after the symlink it takes a little bit of time (<5 sec) for runit to pick up the new service.