autotest: add get_release_version() api to gce_host.py

Lets the tests conveniently get the version of DUT.

BUG=None
TEST=Tested with a server test on lakitu board

Change-Id: Ie5f68b9d543614d76b08bb6f4d9816b5758b2c5b
Reviewed-on: https://chromium-review.googlesource.com/320950
Commit-Ready: Aditya Kali <adityakali@google.com>
Tested-by: Aditya Kali <adityakali@google.com>
Reviewed-by: Daniel Wang <wonderfly@google.com>
1 file changed