Bug 1435031 - Make it easier to use geckoview_example from android_emulator_unittest.py; r=jmaher

In general, there is no simple mapping between apk name (geckoview_example.apk) and
package name (org.mozilla.geckoview_example). With bug 1434411, it will be relatively
easy to add or modify tasks to use a geckoview apk in taskcluster tests. At the
mozharness level, scripts are expected to expand mozharness configurations containing
"%(app)" into package names. For Firefox, android_emulator_unittest extracts and
reads package_name.txt, but there is no such file in the geckoview apk. In future
we might add package_name.txt to the geckoview apk, or possibly use a tool like aapt,
but for our immediate needs this simple hack does the job: If "geckoview" is in
the apk name, assume we are installing org.mozilla.geckoview_example.

testing/mozharness/scripts/android_emulator_unittest.py

@@ -376,6 +376,11 @@ class AndroidEmulatorTest(TestingMixin, EmulatorMixin, BaseScript, MozbaseMixin)
             self.warning("Failed to take screenshot: %s" % err.strerror)
 
     def _query_package_name(self):
+        if self.app_name is None:
+            # For convenience, assume geckoview_example when install target
+            # looks like geckoview.
+            if 'geckoview' in self.installer_path:
+                self.app_name = 'org.mozilla.geckoview_example'
         if self.app_name is None:
             # Find appname from package-name.txt - assumes download-and-extract
             # has completed successfully.