SPARK-1589: Fix the incorrect compare

JIRA: https://issues.apache.org/jira/browse/SPARK-1589

Author: zsxwing <zsxwing@gmail.com>

Closes #508 from zsxwing/SPARK-1589 and squashes the following commits:

570c67a [zsxwing] SPARK-1589: Fix the incorrect compare

(cherry picked from commit 6ab7578067e3bb78b64f99fd67c97e9607050ffe)
Signed-off-by: Reynold Xin <rxin@apache.org>
[Fix #79] Replace Breakable For Loops By While Loops

Author: Sandeep <sandeep@techaddict.me>

Closes #503 from techaddict/fix-79 and squashes the following commits:

e3f6746 [Sandeep] Style changes
07a4f6b [Sandeep] for loop to While loop
0a6d8e9 [Sandeep] Breakable for loop to While loop

(cherry picked from commit bb68f47745eec2954814d3da277a672d5cf89980)
Signed-off-by: Reynold Xin <rxin@apache.org>
SPARK-1587 Fix thread leak

mvn test fails (intermittently) due to thread leak - since scalatest runs all tests in same vm.

Author: Mridul Muralidharan <mridulm80@apache.org>

Closes #504 from mridulm/resource_leak_fixes and squashes the following commits:

a5d10d0 [Mridul Muralidharan] Prevent thread leaks while running tests : cleanup all threads when SparkContext.stop is invoked. Causes tests to fail
7b5e19c [Mridul Muralidharan] Prevent NPE while running tests

(cherry picked from commit dd681f502eafe39cfb8a5a62ea2d28016ac6013d)
Signed-off-by: Aaron Davidson <aaron@databricks.com>