Handle "no such process" during keepalived process cleanup

First, the _stop_keepalived_manager() was doing redundant work of
the KeepalivedManager.disable() method. I.e. SIGTERM pid
wait for 5s and then SIGKILL. Therefore I removed that code from the
test file.
Next, I wrapped the self.manager.disable() to handle for the non atomic
operation of the disable() function where SIGTERM can sometimes stop
the process right before the SIGKILL is called. We dont want this to
fail the test as shown in the linked bug.

Closes-Bug: #2017037
Change-Id: Ide244c079094f60779ce446283e5d51ae15e9af3

neutron/tests/functional/agent/linux/test_keepalived.py

@@ -13,7 +13,6 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
-import signal
 
 from oslo_config import cfg
 
@@ -27,6 +26,7 @@ from neutron.tests.common import net_helpers
 from neutron.tests.functional.agent.linux import helpers
 from neutron.tests.functional import base
 from neutron.tests.unit.agent.linux import test_keepalived
+from neutron_lib.exceptions import ProcessExecutionError
 
 
 class KeepalivedManagerTestCase(base.BaseSudoTestCase,
@@ -51,12 +51,17 @@ class KeepalivedManagerTestCase(base.BaseSudoTestCase,
         self.addCleanup(self._stop_keepalived_manager)
 
     def _stop_keepalived_manager(self):
-        self.manager.disable()
         try:
-            common_utils.wait_until_true(
-                lambda: not self.manager.get_process().active, timeout=5)
-        except common_utils.WaitTimeout:
-            self.manager.get_process().disable(sig=signal.SIGKILL)
+            self.manager.disable()
+        except ProcessExecutionError as process_err:
+            # self.manager.disable() will perform SIGTERM->wait->SIGKILL
+            # (if needed) on the process. However, it is sometimes possible
+            # that SIGKILL gets called on a process that just exited due to
+            # SIGTERM. Ignore this condition so the test is not marked as
+            # failed.
+            if not (len(process_err.args) > 0 and
+                    "No such process" in process_err.args[0]):
+                raise
 
     def _prepare_devices(self):
         # NOTE(slaweq): those are devices used in keepalived config file,