Update mts task to make mts-${MODULE} test suites

In addition to a single mts test suite, we want to have slim, per-module
mts test suites. This introduces the infrastructure to build a test
suite for each module added to mts_modules.

Bug: 170318013
Test: m mts
Test: m mts-tzdata
Change-Id: Ib93ea14e6fa99e362785681cd7660a1ca37e0fe3