Add continuous coverage for Robolectric tests

Configured jacoco build for Robolectric tests, and dist the results
so it can be picked up in continuous testing.

Test: OUT_DIR=/path/to/out DIST_DIR=/path/to/out/dist \
      ./gradlew coverage dist
Bug: 66828854

Change-Id: If847f74dbcfa57af1ce3c64f28c2c870f4b9d973