[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

[runtests] Cleanups.

* Remove "const" on pass-by-value in headers. This is meaningless in
C++. Removal of const makes it clearer that it's pass-by-value.
* Fix some comments in log-exporter.h
* Use getopt instead of hand-rolled argument parsing.
* Fix test summary JSON schema to accurately reflect that syslog may
not always be present.

Test: Existing unit tests. And CQ will use runtests to run other tests.

Bug: IN-478 #done
Change-Id: Id3890a95f61f42f1bc9e1830b2891f689d237a78

[runtests] Create host version of runtests.

-Abstract the current runtests main() as a library method.
-Invoke with platform specific choices for
system/uapp/runtests/runtests.cpp
and
system/host/runtests/runtests.cpp

TESTED: runtests-utils-test passes as a host test; host runtests tested
by hand.

BUG: IN-358
Change-Id: Ic9bf53e4418e37d9856a5857b673f5cbd1fe2d4d