Reduce Docker image size

[simleo]

• reduce number of layers
• run yum clean
• disable pip cache
• run python setup.py clean

BEFORE:
crs4/pydoop-docs      1.92GB
crs4/pydoop           1.53GB
crs4/pydoop-docs-base 1.9GB
crs4/pydoop-base      1.49GB

AFTER:
crs4/pydoop-docs       1.67GB
crs4/pydoop            1.4GB
crs4/pydoop-docs-base  1.65GB
crs4/pydoop-base       1.37GB