[SPARK-19955][PYSPARK] Jenkins Python Conda based test.

## What changes were proposed in this pull request?

Allow Jenkins Python tests to use the installed conda to test Python 2.7 support & test pip installability.

## How was this patch tested?

Updated shell scripts, ran tests locally with installed conda, ran tests in Jenkins.

Author: Holden Karau <holden@us.ibm.com>

Closes #17355 from holdenk/SPARK-19955-support-python-tests-with-conda.