[autotest] Add moblab autotest install directory.

Remove the hardcoding of the moblab autotest install directory,
and have it passed via global_config.

Also point poor_mans_rpc to use get_installed_autodir as a host's
autodir is not set unless ran within autotest.py.

BUG=chromium:405170
TEST=Able to add both Moblab and Non-Moblab DUTs via cli/atest.
Moblab server-side and client-side tests work.

Change-Id: I83be3ed9f1c6d54022063f08e62d6254326a7ace
Reviewed-on: https://chromium-review.googlesource.com/213170
Reviewed-by: Simran Basi <sbasi@chromium.org>
Tested-by: Simran Basi <sbasi@chromium.org>
Commit-Queue: Simran Basi <sbasi@chromium.org>
3 files changed