[gae.py] Allow mixed runtimes as long as they can be deployed using same SDK.
[gae.py] Allow mixed runtimes as long as they can be deployed using same SDK.

This is important when deploying logdog. It will have 'go111' (for GAE Std) and
'go' (for GAE Flex), but they both can be deployed using same toolset, so this
is fine.

R=iannucci@chromium.org, a30c74fa30536fe7ea81ed6dec202e35e149e1fd@chromium.org

Change-Id: Icf36f0018fbff826eba4517bfe5f05f7457edd78
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-py/+/1696217
Reviewed-by: Andrii Shyshkalov <a30c74fa30536fe7ea81ed6dec202e35e149e1fd@chromium.org>
Commit-Queue: Vadim Shtayura <9f116ddb1b24f6fc1916a676eb17161b6c07dfc1@chromium.org>

luci/luci-py,luci/luci-py,luci/luci-py,luci/luci-py