[android] make gradle rootProject.name match the project dir

To fix the gradle error on some platforms:
```
java.lang.IllegalStateException: Module entity with name: openthread_commissioner.app should be available
```

android/openthread_commissioner/settings.gradle

@@ -1,3 +1,3 @@
 include ':service'
 include ':app'
-rootProject.name = "OpenThread Commissioner"
+rootProject.name = "openThread_commissioner"