SPARK-1465: Spark compilation is broken with the latest hadoop-2.4.0 release

YARN-1824 changes the APIs (addToEnvironment, setEnvFromInputString) in Apps, which causes the spark build to break if built against a version 2.4.0. To fix this, create the spark own function to do that functionality which will not break compiling against 2.3 and other 2.x versions.

Author: xuan <xuan@MacBook-Pro.local>
Author: xuan <xuan@macbook-pro.home>

Closes #396 from xgong/master and squashes the following commits:

42b5984 [xuan] Remove two extra imports
bc0926f [xuan] Remove usage of org.apache.hadoop.util.Shell
be89fa7 [xuan] fix Spark compilation is broken with the latest hadoop-2.4.0 release

(cherry picked from commit 725925cf2120e998651f7d1406fdb34fc2405b9f)
Signed-off-by: Thomas Graves <tgraves@apache.org>