logger: only use log transformer in clustered mode

There is no sane way to redirect the stdout/stderr of the current
process in node and that is where apps will log to when not clustered.
Since we cannot process the stdout/stderr of the app to add timestamps
and other tagging, we should disable our own log line prefixing for the
sake of consistency.

SLN-1060 - log cleanup
cluster: use 0 as cluster master's worker id

Make the worker stamping more regular by using worker:0 instead of
worker:supervisor. The clustering support already specifies that 0 is
the predefined "worker" id of the cluster master process and carrying
that into the log output will make it easier to parse and process.

SLN-1060 - log cleanup
Export supervisor's logger in worker processes

Make sure strong-agent gets the supervisor's logger in both worker and
supervisor processes so that log level tagging is done, otherwise the
output is highly inconsistent.

SLN-1060 - log cleanup