Re-enable tests that were disabled due to flakes

[ash211]

See https://github.com/palantir/spark/pull/100/files for the tests that were disabled.

• all Python tests
• all R tests
• 1 network timeout test
• 2 flume tests
• 17 mllib tests
• ~30 hive window query tests
• 2 hive spark submit tests
• 1 date cast test (!)
• 1 parquet datasource summary file test (!) -- correctly enable metadata writing #101