Adds+fixes testHandlesReferencingOtherEntityInPojoFieldsOfOtherTypes (WIP)
Fix sensor-subscription: equals based on name

- previously equality for sensor-subscription matching was on
  `sensor.equals()`, which takes into account name+type+description.
  This breaks things in yaml, where we want to just pass the sensor name.
- Therefore EntitySensorToken using sensor name for equality.
Adds TypeCoercions for String->File

- assumes file will be on local management machine, so does
  `Os.tidyPath`
checkJavaHostnameBug: handle if .profile etc does stdout

- put markers around `hostname` output, so if there is extra stdout
  before or after then that will be ignored.
- hit this warning when using an unusual "brooklyn.ssh.config.scriptHeader"