Speed up Soong integration tests.

This is done by running a build before the first test case, tarring up
$TOP (including out/) then untarring it for every test case instead of
rebuilding soong_build each time.

The speedup is approximately 2x.

Also add some cute ANSI escape sequences and delineation of individual
test cases.

Test: The aforementioned integration tests.
Change-Id: I6a98660cfe6a40bcaa978e8d7544cdffad86a7fa