Allow update_engine to get gsid property

Allow the update_engine to use the gsid property and to avoid the VAB
merge when running a DSU.

Bug:147071959
Test: ota_e2etest.py

Merged-In: I40220877625453198b217e788e6b3bfab8437f24
Change-Id: I40220877625453198b217e788e6b3bfab8437f24
1 file changed