DO NOT MERGE Pack the update_engine_config.txt when using the A/B OTA updater.
This config file pulled directly from the source specifies the update
payload version supported by the code. When generating an incremental
update payload for the A/B updater, the generated payload format will
match the version supported by the old version.
Bug:
24406755
Test: `make dist` on Brillo.
Change-Id: Ib7ac6828d0d34eb31e786dbaae5d59ecf26c3576
(cherry picked from commit
70067acd663df3fb0a747085f3d928c4b1777154)