Osu2: add class for managing Wi-Fi network connection

Also setup a test app for unit tests, with few test
cases added for NetworkConnection.

Bug: 62388032
Test: start OSU app with Boigno OSU provider via adb,
      verify the OSU app is started and connected to
      the Boingo OSU AP.
Test: frameworks/base/packages/Osu2/tests/runtests.sh

Change-Id: Id60bc85871f3251d83d779d430e1dd1eff47d86e