test: delete STRONGLOOP_METRICS after each test

Leaving an invalid STRONGLOOP_METRICS in the environment causes
subsequent tests to fail.
run: directly support statsd backends

For new metrics URL formats, start a statsd child process, and use it to
deliver metrics to (at this moment) splunk, console, graphite, and
syslog.
Expose worker log transformer/wrapper via config
Use --log mechanism for statsd process
run: exit if metrics URL is invalid