Actually added pretest support

Actually added pretest support
And reverted mistake

BUG=453174
TBR=iannucci@chromium.org

Committed: https://chromium.googlesource.com/infra/testing/expect_tests/+/b6c4c94d63377cbd38b184af9794699e759339a8

[pgervais, 2015-02-03 02:13:19]

Committed patchset #2 (id:20001) manually as
b6c4c94d63377cbd38b184af9794699e759339a8 (presubmit successful).

[agable, 2015-02-03 04:23:48]

agable@chromium.org changed reviewers:
+ agable@chromium.org

[agable, 2015-02-03 04:23:49]

https://codereview.chromium.org/892363002/diff/20001/expect_tests/pipeline.py
File expect_tests/pipeline.py (right):

https://codereview.chromium.org/892363002/diff/20001/expect_tests/pipeline.py...
expect_tests/pipeline.py:402: pretest_filename =
os.path.join(processing_context.cwd, '.expect_tests.py')
In the documentation you committed previously, you named this file
".expect_tests_pretest.py".

[agable, 2015-02-03 04:27:59]

https://codereview.chromium.org/892363002/diff/20001/expect_tests/pipeline.py
File expect_tests/pipeline.py (right):

https://codereview.chromium.org/892363002/diff/20001/expect_tests/pipeline.py...
expect_tests/pipeline.py:402: pretest_filename =
os.path.join(processing_context.cwd, '.expect_tests.py')
On 2015/02/03 04:23:48, agable wrote:
> In the documentation you committed previously, you named this file
> ".expect_tests_pretest.py".

Also, this implementation requires the same .expect_tests.py file to be in every
subdirectory of appengine/. This makes me sad, but I understand why it is that
way.

[agable, 2015-02-03 04:31:00]

On 2015/02/03 04:27:59, agable wrote:
> https://codereview.chromium.org/892363002/diff/20001/expect_tests/pipeline.py
> File expect_tests/pipeline.py (right):
> 
>
https://codereview.chromium.org/892363002/diff/20001/expect_tests/pipeline.py...
> expect_tests/pipeline.py:402: pretest_filename =
> os.path.join(processing_context.cwd, '.expect_tests.py')
> On 2015/02/03 04:23:48, agable wrote:
> > In the documentation you committed previously, you named this file
> > ".expect_tests_pretest.py".
> 
> Also, this implementation requires the same .expect_tests.py file to be in
every
> subdirectory of appengine/. This makes me sad, but I understand why it is that
> way.

[agable, 2015-02-03 04:32:10]

Final message I think: When the .expect_tests.py file is execfiled, it's
__file__ attribute is
ENV/local/lib/python2.7/site-packages/expect_tests/pipeline.pyc. So locating the
appengine sdk directory that should be added to PYTHONPATH is harder.