Bug 1395718 - In devicemanager killProcess, only use force-stop when a signal is not specified; r=bc

dm.killProcess correctly tries to use 'am force-stop' in preference to kill()
to end a process. But some clients of killProcess specify a kill signal and
use killProcess for purposes other than endding the process, for example, to trigger
crash dumps. To allow for these cases, it is better to not use force-stop when a
signal is specified.

testing/mozbase/mozdevice/mozdevice/devicemanagerADB.py

@@ -444,11 +444,12 @@ class DeviceManagerADB(DeviceManager):
         return outputFile
 
     def killProcess(self, appname, sig=None):
-        try:
-            self.shellCheckOutput(["am", "force-stop", appname], timeout=self.short_timeout)
-        except:
-            # no problem - will kill it instead
-            self._logger.info("killProcess failed force-stop of %s" % appname)
+        if not sig:
+            try:
+                self.shellCheckOutput(["am", "force-stop", appname], timeout=self.short_timeout)
+            except:
+                # no problem - will kill it instead
+                self._logger.info("killProcess failed force-stop of %s" % appname)
 
         shell_args = ["shell"]
         if self._sdk_version >= version_codes.N: