Unit test fixes for SDK update

Summary:
There's a weird interaction with Eclipse generated files in the latest Android SDK update that is preventing Ant from building projects unless they're cleaned first.
Also made unit tests run on the first device returned from `adb devices` if there are multiple devices plugged in. This keeps the unit test engine from waiting around for you to unplug a device. If there are no devices detected, it will also now tell you to plug one in. (T4656)

Test Plan: Run unit tests with multiple devices plugged in.

Reviewers: mportune, mbishop

Reviewed By: mportune

CC: jstarke, gsaintjean

Differential Revision: https://devportal.imobile3.com/D4890