Configure your libgdx Android Manifest like this and specify both min and target sdk version:
<uses-sdk android:minSdkVersion="5" android:targetSdkVersion="19" />
You can use API 5 as the minimum android version as this is what libgdx still supports. Don't get confused about the meaning of the target sdk version: this basically means that you have tested it against latest android version, it doesn't mean that it won't run on previous versions, because you have specified a min sdk before. Rule of thumb: put min-sdk as low as possible and target-sdk as high as possible.
Configuring it that way your game should still run in old devices and using configChanges like this will work as well:
android:configChanges="keyboard|keyboardHidden|orientation|screenSize"
I have just recently launched a game with configurations like this and works like a charm even on Gingerbread ;-)