I used 10.0.2.2 successfully on my home machine, but at work, it did not work. After hours of fooling around, I created a new emulator instance using the Android Virtual Device (AVD) manager, and finally the 10.0.2.2 worked.
I don't know what was wrong with the other emulator instance (the platform was the same), but if you find 10.0.2.2 does not work, try creating a new emulator instance.