internal: use persisted environment for --metrics

Move the STRONGLOOP_METRICS environment variable out of the Upstart job
and into the initial persisted environment.
docs: update command usage sections
pm: exit on parent ipc disconnect
add ServiceMetric model
server: ServiceProcess processId rename to pid
fixup! fake metrics generation

use `slc pm -F` to generate fake data
fixup! fake metrics in process
rest: expose metrics at top-level
model: executor, instance, process exposed
WIP, get live metrics