Bug 1062228 - Set re.IGNORECASE correctly for the build_type regex

Only the re module function .search() accepts the flags argument, for
the regexobject search() method it actually gets interpreted as the
'pos' parameter, since |re.IGNORECASE == 2|.

With this change we now correctly identify tests run on ASAN builds as
buildtype 'asan'.
Merge pull request #198 from mozilla/buildtype

Set re.IGNORECASE correctly for the build_type regex (bug 1062228)
Bug 1061758 - Suppress the job name from Mochitest-OOP symbols too

Treeherder equivalent of:
https://hg.mozilla.org/webtools/tbpl/rev/718d944e6511#l3.13
Bug 1062579 - Ensure get_symbol() cannot return an empty job symbol

In the case where 'n' wasn't found for jobs whose symbol letter was
suppressed (eg: a mochitest job that isn't split into multiple parts),
get_symbol() could have previously returned an empty symbol.
The suppression now only takes place if 'n' was found.
Bug 1060339 - Parse logs for error lines even if the job was successful

In an ideal world, we would never have a successful job that contained
errors which our log parser regex matched against. Unfortunately this is
not the case in practice, since:

1) There is sometimes spammy log output that isn't intended to make the
   job fail, but which false-positive matches against our log regex.
2) Sometimes the test/harness/buildbot/... is broken and the log error
   is real, and it should have caused the run to fail.

In the case of #1, hiding these errors in successful runs means that
when someone looks at the error summary for a failed run, they don't
realise that a proportion of the failures they can see are actually
present in _every_ job, not just the failed ones.

In the case of #2, hiding the errors means we don't realise <foo> is
broken and needs fixing.

As such, we now parse for error lines in all jobs, including successful.