lorax-composer: Cancel running Anaconda process

It ends up that this isn't as easy as you'd think. Anaconda sets up some
signal handlers to handle cleanly exiting, but they are not being run
when sent a TERM after package installation has started. I think DNF
resets them causing it to get ignored.

When the cancel is sent it can take several minutes for it to have an
effect. In my testing it usually takes around 2 minutes for anaconda to
notice and exit.

This sends a TERM to the process and then waits for it to exit. When it
returns it then removed any device-mapper devices that were setup for
image installations, removes any hanging loop devices.

It then kills off any process with pyanaconda. in the cmdline, and
anaconda-bus.conf (because anaconda starts a bunch of helpers and if it
doesn't shut down cleanly they remain running).

Resolves: rhbz#1656691

src/pylorax/installer.py

@@ -21,9 +21,9 @@ import glob
 import json
 from math import ceil
 import os
-import subprocess
 import shutil
 import socket
+import subprocess
 import tempfile
 
 # Use the Lorax treebuilder branch for iso creation
@@ -285,7 +285,10 @@ def novirt_cancel_check(cancel_funcs, proc):
     """
     for f in cancel_funcs:
         if f():
+            log.info("Terminating process %d", proc.pid)
             proc.terminate()
+
+            # NOTE: Have to return and allow execReadlines to call proc.communicate()
             return True
     return False
 
@@ -386,6 +389,7 @@ def novirt_install(opts, disk_img, disk_size, cancel_func=None):
         for line in execReadlines("anaconda", args, reset_lang=False,
                                   env_add={"ANACONDA_PRODUCTNAME": opts.project,
                                            "ANACONDA_PRODUCTVERSION": opts.releasever},
+                                  reset_handlers=False,
                                   callback=lambda p: not novirt_cancel_check(cancel_funcs, p)):
             log.info(line)
 
@@ -441,6 +445,12 @@ def novirt_install(opts, disk_img, disk_size, cancel_func=None):
             log.debug("Removing loop device for %s", disk_img)
             loop_detach("/dev/"+get_loop_name(disk_img))
 
+        # When anaconda crashes or is canceled it leaves pyanaconda.* running
+        execWithRedirect("pkill", ["-f", "pyanaconda."])
+
+        # It can also leave dbus running
+        execWithRedirect("pkill", ["-f", "anaconda-bus.conf"])
+
     # qemu disk image is used by bare qcow2 images and by Vagrant
     if opts.image_type:
         log.info("Converting %s to %s", disk_img, opts.image_type)