Send SIGTERM repeatedly to terminate trillian processes

Repeated kill is a workaround that can most likely be reverted once
google/trillian#2805 makes into into a
trillian release.

Uses SIGTERM rather than SIGINT, because (i) SIGTERM (the default kill
signal) seems more appropriate for scripted usage, while SIGINT is for
interactive usage, e.g., pressing Control-C in the terminal, and (ii)
SIGINT didn't work in my local tests.

integration/test.sh

@@ -329,11 +329,19 @@ function node_stop_fe() {
 
 function node_stop_be() {
 	for i in $@; do
-		pp ${nvars[$i:tsrv_pid]} && kill -2 ${nvars[$i:tsrv_pid]}
+		pp ${nvars[$i:tsrv_pid]} && kill ${nvars[$i:tsrv_pid]}
 		while :; do
 			sleep 1
 
-			pp ${nvars[$i:tsrv_pid]} && continue
+			# The Trillian log server doesn't exit
+			# properly on first SIGTERM, so we repeat it,
+			# rather than just waiting for the process to
+			# shut down.
+			if pp ${nvars[$i:tsrv_pid]}; then
+				info "Resending SIGTERM to process ${nvars[$i:tsrv_pid]}"
+				kill ${nvars[$i:tsrv_pid]}
+				continue
+			fi
 
 			break
 		done