Bug 1516985 - Uninstall Firefox Android app prior to installation to prevent INSTALL_FAILED_UPDATE_INCOMPATIBLE errors, r=davehunt

Differential Revision: https://phabricator.services.mozilla.com/D36936

--HG--
extra : moz-landing-system : lando

testing/mozharness/mozharness/mozilla/testing/raptor.py

@@ -506,6 +506,7 @@ class Raptor(TestingMixin, MercurialScript, CodeCoverageMixin, AndroidMixin):
 
     def install(self):
         if self.app in self.firefox_android_browsers:
+            self.device.uninstall_app(self.binary_path)
             self.install_apk(self.installer_path)
         else:
             super(Raptor, self).install()