Support log templating for supervisor log name

Substitutes 'supervisor' for worker ID, and pid is of the invoking process, not the detached master
Ensure cluster uses correct args for children

v0.10.x works fine without this change, but v0.11.x grabs the
contents of process.args when cluster is first loaded, so it must
be set explicitly.

See joyent/node#7670
Use strong-log-transformer for log tagging

Currently defaults to always timestamping and tagging with pid and
worker id.

Change --log option to work independantly of --detach.
Re-open logfiles on SIGUSR2
Make default log name work non-detached

Previously --detach triggered logging, but it is now independant.
Don't close supervisor log on worker exit

If the log sink is a shared stream don't propagate 'end' events to it
Use a simple logger for supervisor logs

Messages are redirected to the specified log file if/when it becomes available
Log reopening of log files