Minor gradle updates, due to Android L.

- Build tools update to latest version (20).
- testPackageName is correctly calculated by default, doing nothing.
- support library needs some tweaks to support pre Android L versions.
We don't need support library from Robotium.

I've also fixed a simple test that wasn't letting the suite to finish
correctly.
Simulate network down.

The tests say they failed, but it's because the adb server is no longer
able to communicate with the emulator due to switching network
connectivity off (and being the adb server connected to a local tcp port
of the emulator, this port dissapears once connectivity is down).

To see if all tests passed, take a look at the logcat.
Once tests are finished, issue "adb kill-server" from the development
machine, and then "adb logcat".
network up & down 3 times: sometimes fails

I simulate removing the network at the end of the test.

Sometimes, the test fails because a openvpn tries to close a bad file
descriptor.
Some instructions to run the tests.
Merge branch 'feature/Fix-existing-network-failure-tests-and-add-more-#3724' into develop