Implemented testing connection to device and its unit tests.

To implement the base performance test, we first have to
implement connecting to the device. Introduced the
--serial argument to the argument parser in torq.py,
implemented the get_adb_devices and check_device_connection
APIs of AdbDevice in device.py, and implemented 11 unit
tests in tests/device_unit_test.py to test these 2 new APIs.

Test: atest device_unit_test
Bug: 355053544

Change-Id: I75e3430f28b92b6978a270ccded72690af29d312
5 files changed