python-adb: Add support for devices that need_su to attain root privileges.

Molded after https://codesearch.chromium.org/chromium/src/third_party/catapult/devil/devil/android/device_utils.py?rcl=2dd914402ebcc44ecb60034e5c7b9bfa3d0c9d89&l=462

Bug: 780559
Change-Id: I2c32ee8219d897301dc76cc114513b5c9fb52763
Reviewed-on: https://chromium-review.googlesource.com/c/1260622
Reviewed-by: Marc-Antoine Ruel <maruel@chromium.org>
2 files changed