btest-bg-run-helper: Ignore SIGTERM to self during cleanup

The kill 0 invocation would kill the btest-bg-run-helper itself,
causing the subsequent logic to not be executed, resulting in
runaway processes on the system.

Author: awelzel

btest-bg-run-helper

@@ -3,8 +3,19 @@
 # Internal helper for btest-bg-run.
 
 cleanup() {
+    # Ignore SIGTERM during cleanup to prevent terminating
+    # this process when sending signals to the process group.
+    trap true SIGTERM
+
     if [ ! -e .exitcode ]; then
         echo 15 >.exitcode
+
+        # Send SIGTERM to all processes in the process group
+        # of the calling process.
+        #
+        # This should terminate any well-behaved background
+        # commands that were spawned by the program under test
+        # unless they started their own process group.
         kill 0 &>/dev/null
 
         if [ -n "$pid" ]; then