SPARK-1707. Remove unnecessary 3 second sleep in YarnClusterScheduler

Author: Sandy Ryza <sandy@cloudera.com>

Closes #634 from sryza/sandy-spark-1707 and squashes the following commits:

2f6e358 [Sandy Ryza] Default min registered executors ratio to .8 for YARN
354c630 [Sandy Ryza] Remove outdated comments
c744ef3 [Sandy Ryza] Take out waitForInitialAllocations
2a4329b [Sandy Ryza] SPARK-1707. Remove unnecessary 3 second sleep in YarnClusterScheduler
[SPARK-2494] [PySpark] make hash of None consistant cross machines

In CPython, hash of None is different cross machines, it will cause wrong result during shuffle. This PR will fix this.

Author: Davies Liu <davies.liu@gmail.com>

Closes #1371 from davies/hash_of_none and squashes the following commits:

d01745f [Davies Liu] add comments, remove outdated unit tests
5467141 [Davies Liu] disable hijack of hash, use it only for partitionBy()
b7118aa [Davies Liu] use __builtin__ instead of __builtins__
839e417 [Davies Liu] hijack hash to make hash of None consistant cross machines
Fix flakey HiveQuerySuite test

Result may not be returned in the expected order, so relax that constraint.

Author: Aaron Davidson <aaron@databricks.com>

Closes #1514 from aarondav/flakey and squashes the following commits:

e5af823 [Aaron Davidson] Fix flakey HiveQuerySuite test