Case for this is:

suite.testA is run, the data comes back is one of the three

suite.PRE_testA P
suite.testA P or F

suite.PRE_testA F
suite.testA missing!

to fix this, if suite.testA is missing treat suite.PRE_testA as suite.testA

The following revision refers to this bug:
  https://chromium.googlesource.com/infra/infra/+/eecfb6d2aeb7fb4f5b8e74c2051e6e7afc5cbeca

commit eecfb6d2aeb7fb4f5b8e74c2051e6e7afc5cbeca
Author: Brandon Wylie <wylieb@chromium.org>
Date: Thu Apr 12 22:48:24 2018

[Findit] Flake Analyzer - Add support for PRE_test runs

Right now we assume that there is only one test reslt in test results,
which isn't true in the case where the test has a PRE_test hook.

This CL adds support for three cases
1. No prerun, and test results exist.
2. Prerun, but test results exist.
3. Prerun and no test results exist.

Bug: 832158
Change-Id: I4888dc87436926e98f361a2afea2e6e8a77a458b
Reviewed-on: https://chromium-review.googlesource.com/1010832
Commit-Queue: Brandon Wylie <wylieb@chromium.org>
Reviewed-by: Shuotao Gao <stgao@chromium.org>

[modify] https://crrev.com/eecfb6d2aeb7fb4f5b8e74c2051e6e7afc5cbeca/appengine/findit/services/flake_failure/test/flake_swarming_test.py
[modify] https://crrev.com/eecfb6d2aeb7fb4f5b8e74c2051e6e7afc5cbeca/appengine/findit/services/flake_failure/flake_swarming.py