Remove references to ClusterScheduler (SPARK-1140)

ClusterScheduler was renamed to TaskSchedulerImpl; this commit
updates comments and tests accordingly.

Author: Kay Ousterhout <kayousterhout@gmail.com>

Closes #9 from kayousterhout/cluster_scheduler_death and squashes the following commits:

d6fd119 [Kay Ousterhout] Remove references to ClusterScheduler.
SPARK-1129: use a predefined seed when seed is zero in XORShiftRandom

If the seed is zero, XORShift generates all zeros, which would create unexpected result.

JIRA: https://spark-project.atlassian.net/browse/SPARK-1129

Author: Xiangrui Meng <meng@databricks.com>

Closes #645 from mengxr/xor and squashes the following commits:

1b086ab [Xiangrui Meng] use MurmurHash3 to set seed in XORShiftRandom
45c6f16 [Xiangrui Meng] minor style change
51f4050 [Xiangrui Meng] use a predefined seed when seed is zero in XORShiftRandom