Kill all subprocess in signal handler

When Pungi receives a signal to terminate, it can sometimes get stuck
if there are threads running. It has to wait for all worker threads to
finish. They generally do finish, unless they get stuck waiting on a
subprocess.

This patch should reduce the likelihood of this happening by stopping
all subprocesses.

JIRA: RHELCMP-3056
Signed-off-by: Lubomír Sedlář <lsedlar@redhat.com>

pungi/scripts/pungi_koji.py

@@ -14,6 +14,7 @@ import signal
 import sys
 import traceback
 import shutil
+import subprocess
 
 from six.moves import shlex_quote
 
@@ -581,8 +582,20 @@ def run_compose(
     compose.log_info("Compose finished: %s" % compose.topdir)
 
 
+def try_kill_children(signal):
+    try:
+        if COMPOSE:
+            COMPOSE.log_warning("Trying to kill all subprocesses")
+        pid = os.getpid()
+        subprocess.call(["pkill", "-P", str(pid)])
+    except Exception:
+        if COMPOSE:
+            COMPOSE.log_warning("Failed to kill all subprocesses")
+
+
 def sigterm_handler(signum, frame):
     if COMPOSE:
+        try_kill_children(signum)
         COMPOSE.log_error("Compose run failed: signal %s" % signum)
         COMPOSE.log_error("Traceback:\n%s" % "\n".join(traceback.format_stack(frame)))
         COMPOSE.log_critical("Compose failed: %s" % COMPOSE.topdir)