HOTFIX: Fix Python tests on Jenkins.

Author: Patrick Wendell <pwendell@gmail.com>

Closes #1036 from pwendell/jenkins-test and squashes the following commits:

9c99856 [Patrick Wendell] Better output during tests
71e7b74 [Patrick Wendell] Removing incorrect python path
74984db [Patrick Wendell] HOTFIX: Allow PySpark tests to run on Jenkins.
(cherry picked from commit fb499be1ac935b6f91046ec8ff23ac1267c82342)

Signed-off-by: Patrick Wendell <pwendell@gmail.com>