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ARROW-561:[JAVA][PYTHON] Update java & python dependencies to improve downstream packaging experience

The current build for arrow uses a interesting work around for hamcrest conflict between JUNIT and mockito which results in mockito being in the compile scope. This is not suitable for some downstream users.

Python setup file also leaves out test dependency (not overly important but useful for developers) & we can clarify parquet-cpp as an "extra" dependency for people requiring parquet support (already mentioned in the README file but good to have clarity in setup.py as well).

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

Closes #342 from holdenk/ARROW-561-improve-deps and squashes the following commits:

5919b32 [Holden Karau] Drop extras_requires
938ed97 [Holden Karau] Mention test requires pytest and add an extra requires for parquet
283d6cd [Holden Karau] Remove mockito from compile scope and fix hamcrest issue with exclusion rule instead