SPARK-1417: Spark on Yarn - spark UI link from resourcemanager is broken

Author: Thomas Graves <tgraves@apache.org>

Closes #344 from tgravescs/SPARK-1417 and squashes the following commits:

c450b5f [Thomas Graves] fix test
e1c1d7e [Thomas Graves] add missing $ to appUIAddress
e982ddb [Thomas Graves] use appUIHostPort in appUIAddress
0803ec2 [Thomas Graves] Review comment updates - remove extra newline, simplify assert in test
658a8ec [Thomas Graves] Add a appUIHostPort routine
0614208 [Thomas Graves] Fix test
2a6b1b7 [Thomas Graves] SPARK-1417: Spark on Yarn - spark UI link from resourcemanager is broken