make avd install work under py3
make avd install work under py3

Fix str/bytes type mismatch,
now avd install followed by avd start works under both py2 and py3

Bug: chromium:1187234
Change-Id: I37cf763e0b845e4f7150e909902e782e1b2bdf23
Reviewed-on: https://chromium-review.googlesource.com/c/catapult/+/2753328
Reviewed-by: Dirk Pranke <6693ee08b084bb2ffa767f664c99b689395e0e4b@google.com>
Reviewed-by: Ben Pastene <e214258550f76fa23ac7c1d953424f3f468f5c6b@chromium.org>
Commit-Queue: Weizhong Xia <648e350bf5aac34be4f9d39c9e464cb7b2615f2b@google.com>

catapult-project/catapult,catapult-project/catapult,catapult-project/catapult,catapult-project/catapult,catapult-project/catapult,catapult-project/catapult,catapult-project/catapult