Update the Connectivity Manager test suit to use InstrumentationTestCase.

- Remove ConnectivityManagerTestActivity as the test activity could be destroyed
  after a system config change, which cause test failure in the wifi stress test.
- Update all tests to use InstrumentationTestCase, which instruments the test package.

Bug : 10426067

Change-Id: Ibf6f1f7cffd7a7eabc4cc63c7e033b59274b724e