Prevent certificate issues when installing STFService by uninstalling it first.

lib/roles/device/resources/service.js

@@ -69,10 +69,15 @@ module.exports = syrup.serial()
         })
         .catch(function() {
           log.info('Installing STFService')
-          return promiseutil.periodicNotify(
-              adb.install(options.serial, resource.apk)
-            , 10000
-            )
+          // Uninstall first to make sure we don't have any certificate
+          // issues.
+          return adb.uninstall(options.serial, resource.pkg)
+            .then(function() {
+              return promiseutil.periodicNotify(
+                adb.install(options.serial, resource.apk)
+              , 10000
+              )
+            })
             .progressed(function() {
               log.warn(
                 'STFService installation is taking a long time; '