Add option `--dist` to `test/testrunner/testrunner.py`.

When invoked with this option, `test/testrunner/testrunner.py` adds
`dist` to the build command line (if any).

Also, have `test/testrunner/run_build_test_target.py` pass `--dist` to
`test/testrunner/testrunner.py` for the case of run-tests, when the
`DIST_DIR` environment variable is set.

Test: Rely on `master-art-host` build/test targets.
Bug: 157656545
Change-Id: I30a5a2971494553708c358c1429249f69721da87
2 files changed