Add new simplified lunch function (lunch2)

Includes tests for envsetup.sh

After we've tried this for a bit and are happy, this will be swapped out
to become the new standard lunch and all of the menus and stuff will be
removed.

Test: build/make/tools/envsetup/run_envsetup_tests
Change-Id: Idebeeb1153406238b6c32f3f564c7bc1e7ced7e6