Fixed errors caused by unavailable devices during integration tests

AbstractEmulatorMojo:
Wait until the device has booted

AbstractEmulatorMojoTest:
Expect calls to IDevice.getPropertySync() (now used in AbstractEmulatorMojo)
Removed ./wait_for_emulator
Fixed update of system image: 'sysimg-19' -> 'system-image'
Merge pull request #3 from soggier/travis-config

travis config adaptations/fixes
Merge pull request #396 from soggier/master

Wait for devices to boot, travis config adaptations