Fixup python integration tests under ci.

Release the lock for the pytest task as is done for the junit task
and other code-run tasks (run, repl).

Convert ci to use the pytest task (test goal) and eliminate dup
runs of python tests by restricting the jvm tests to just the
jvm targets.

This change also adds pass-through args for pytest to aid debugging
tests and otherwise running them.  When using this to un-suppress
pytest output, a second form of test blocking was uncovered with
the stdin 'yes' plumbing not working properly.  As a result this
change tweaks the IT in question to use a more robust method of stdin
piping to the pants subprocess.

Testing Done:
1st reproed IT test lock under the test goal (worked find under old build command test runner).

Python tests run once (normal and IT), and they no longer block.
$ ./build-support/bin/ci.sh

Also confirmed the it works with output un-suppressed:
$ PANTS_DEV=1 ./pants goal test tests/python/pants_test:integration --test-pytest-options="-v -s"
...
12:56:36 00:01   [test]
12:56:36 00:01     [pytest]
12:56:36 00:01       [run]
                     *** Running pants in dev mode from /home/jsirois/dev/3rdparty/jsirois-pantsbuild-pants2/src/python/pants/bin/pants_exe.py ***
                     ============== test session starts ===============
                     platform linux3 -- Python 2.6.8 -- py-1.4.20 -- pytest-2.5.2 -- /home/jsirois/dev/3rdparty/pyenv/versions/2.6.8/bin/python
                     plugins: cov, timeout
                     collected 2 items

                     tests/python/pants_test/tasks/test_jar_publish_integration.py:25: JarPublishIntegrationTest.test_java_publish Loading pants backends from source

                     12:56:38 00:00 [main]
                                    See a report at: http://localhost:37586/run/pants_run_2014_06_10_12_56_38_23
...
                     12:56:44 00:06     [jar_create_publish]
                     12:56:44 00:06       [jar-create]....
                     12:56:46 00:08     [publish]Skipping check for a clean jsirois/travis/it_unblock in test mode.

                     Changes for com.pants.examples#hello-greet since 0.0.0 @ None:

                     commit 7c56621a9c4e8a3aca2bee567d77e5a13b6f8a3b
                     Author: Benjy <benjy@foursquare.com>
                     Date:   Tue Apr 1 02:34:30 2014 +0000

                         Introduce java examples.

                      .../hello/greet/Greeting.java    | 13 ++++++++++
                      1 file changed, 13 insertions(+)

                     12:56:46 00:08       [jar-publish]
                                    Waiting for background workers to finish.
                                    SUCCESS*** Running pants in dev mode from /home/jsirois/dev/3rdparty/jsirois-pantsbuild-pants2/src/python/pants/bin/pants_exe.py ***

                     PASSED

...

Bugs closed: 201

Reviewed at https://rbcommons.com/s/twitter/r/478/