Move sigterm_method to zuul.conf

Instead of using an environment variable for this particular
setting, do what we do for every other aspect of Zuul behavior:
use a setting in zuul.conf.

Change-Id: I5c075dce5b6ad23adc863252af67d7ee7ad0d4d5

doc/source/discussion/components.rst

@@ -865,6 +865,21 @@ The following sections of ``zuul.conf`` are used by the executor:
       perform merge operations for any events. The executor will still perform
       the merge operations required for the build they are executing.
 
+   .. attr:: sigterm_method
+      :default: graceful
+
+      Determines how the executor responds to a ``SIGTERM`` signal.
+
+      .. value:: graceful
+
+         Stop accepting new jobs and wait for all running jobs to
+         complete before exiting.
+
+      .. value:: stop
+
+         Abort all running jobs and exit as soon as possible.
+
+
 .. attr:: keystore
 
    .. attr:: password
@@ -929,9 +944,7 @@ running on the stopped executor will be rescheduled on other executors.
 
 The executor normally responds to a ``SIGTERM`` signal in the same way
 as the ``graceful`` command, however you can change this behavior to match
-``stop`` by setting the environment variable
-``ZUUL_EXECUTOR_SIGTERM_METHOD`` to ``stop`` (the default is
-``graceful``).
+``stop`` with the :attr:`executor.sigterm_method` setting.
 
 To enable or disable running Ansible in verbose mode (with the
 ``-vvv`` argument to ansible-playbook) run ``zuul-executor verbose``

releasenotes/notes/graceful-09c7267360190f7a.yaml

@@ -1,13 +1,13 @@
 ---
 features:
   - |
-    The executor now honors the ``ZUUL_EXECUTOR_SIGTERM_METHOD``
-    environment variable to determine whether ``SIGTERM`` should be
+    The executor now honors the :attr:`executor.sigterm_method`
+    configuration file setting to determine whether ``SIGTERM`` should be
     equivalent to the ``graceful`` command (the default) or the
     ``stop`` command.
 upgrade:
   - |
     The default behavior when an executor receives SIGTERM has been
     changed from immediately stopping jobs to gracefully waiting for
-    them to finish.  Set the ``ZUUL_EXECUTOR_SIGTERM_METHOD``
-    environment variable to ``stop`` to preserve the old behavior.
+    them to finish.  Set the :attr:`executor.sigterm_method`
+    configuration file setting to ``stop`` to preserve the old behavior.

zuul/cmd/executor.py

@@ -44,14 +44,18 @@ class Executor(zuul.cmd.ZuulDaemonApp):
             self.args.nodaemon = True
 
     def exit_handler(self, signum, frame):
-        graceful = os.environ.get('ZUUL_EXECUTOR_SIGTERM_METHOD', 'graceful')
+        if self.config.has_option('executor', 'sigterm_method'):
+            graceful = self.config.get('executor', 'sigterm_method')
+        else:
+            graceful = 'graceful'
         if graceful.lower() == 'graceful':
             self.executor.graceful()
         elif graceful.lower() == 'stop':
             self.executor.stop()
         else:
-            self.log.error("Unknown value for ZUUL_EXECUTOR_SIGTERM_METHOD:"
+            self.log.error("Unknown value for executor.sigterm_method:"
                            f"'{graceful}'. Expected 'graceful' or 'stop'")
+            self.executor.graceful()
 
     def start_log_streamer(self):
         pipe_read, pipe_write = os.pipe()