Filtering by status file split to four parts:
1. Getting outcomes - reads both variant dependent and
independent outcomes, no more need to do it twice.
2. Checking unused rules - has a switch to check only variant
dependent/independent rules.
3. Reading flags - if outcome starts with '--' it is treated as a flag.
4. Actual filtering.

Outcomes removed from the testcase object, can be accessed
by call to its testsuite.

Bug: v8:6917
Cq-Include-Trybots: master.tryserver.v8:v8_linux_noi18n_rel_ng
Change-Id: I35762f891010ddda926250452b88656047433daa
Reviewed-on: https://chromium-review.googlesource.com/775160
Commit-Queue: Michał Majewski <majeski@google.com>
Reviewed-by: Sergiy Byelozyorov <sergiyb@chromium.org>
Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49547}