[runtests] Support publishing data through sinks

This enables persisting data published through sanitizer data sink and
publishing them through summary.json file. The loader service is only
changed when the output directory is set and the output directory is
used as the data sink path.

TC-27

Test: runtests-utils
Change-Id: Id76037451a79bf247d8f07046b1f7d8f6ee0c773