env/freebsd-amd64: exit daemon when bootstrapswarm has a zero exit code

Part of the contract of running swarming_bot is that we need to keep
restarting it if it has a non-zero exit code. But if it has a zero exit
code, we must NOT restart it. Currently the daemon just always keeps
restarting it.

Do this by writing the pid of the daemon supervisor and using that to
kill the supervisor when we get a zero exit code from bootstrapswarm.
bootstrapswarm will exit with a zero exit code only if swarming_bot
does.

For golang/go#61095.

Change-Id: I92bdea3fa35fed0883cd9e996aa231e26cdb7155
Reviewed-on: https://go-review.googlesource.com/c/build/+/622040
Auto-Submit: Michael Knyszek <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Dmitri Shuralyov <[email protected]>
Reviewed-by: Dmitri Shuralyov <[email protected]>

Author: mknyszek

env/freebsd-amd64/buildlet

@@ -10,8 +10,9 @@ rcvar=buildlet_enable
 
 procname=/buildlet
 pidfile="/var/run/${name}.pid"
+suppidfile="/var/run/${name}-sup.pid"
 command=/usr/sbin/daemon
-command_args="-r -fc -p ${pidfile}"
+command_args="-r -fc -p ${pidfile} -P ${suppidfile}"
 command_args="${command_args} ${procname}"
 start_precmd="${name}_prestart"
 stop_cmd=":"
@@ -43,7 +44,7 @@ buildlet_prestart()
 		swarming="${swarming}.appspot.com"
 		info "Found Swarming host ${swarming}."
 
-		buildletsh="#!/bin/sh\n\nset -x\n\nsu -l swarming -c \"/usr/local/bin/bootstrapswarm --hostname $gcehost --swarming $swarming\"\n"
+		buildletsh="#!/bin/sh\n\nset -x\n\nsu -l swarming -c \"/usr/local/bin/bootstrapswarm --hostname $gcehost --swarming $swarming && kill -s INT \$(cat $suppidfile)\"\n"
 		echo -e $buildletsh >/buildlet
 	  ;;
 	  *)