Some drain scripts send signals directly to the process via the
PID from the pidfile (because bpm doesn't have a mechanism to
send e.g. a USR1 signal). This obviously only works when the drain
runs inside the same container as the process itself.

This commit maintains a pid file at the /var/vcap/sys/run/bpm/$JOB/$PORC.pid
location and also implements the `bpm pid` command to access it.

Signed-off-by: Jan Dubois <[email protected]>

Signed-off-by: Jan Dubois <[email protected]>

The pid is unused by the rest of the tests, so for now just set
it to 0.

Signed-off-by: Jan Dubois <[email protected]>