Fix UISuite unit test that fails under Jenkins contention

Due to perhaps zombie processes on Jenkins, it seems that at least 10
Spark ports are in use. It also doesn't matter that the port increases
when used, it could in fact go down -- the only part that matters is
that it selects a different port rather than failing to bind.
Changed test to match this.

Thanks to @andrewor14 for helping diagnose this.

Author: Aaron Davidson <aaron@databricks.com>

Closes #857 from aarondav/tiny and squashes the following commits:

c199ec8 [Aaron Davidson] Fix UISuite unit test that fails under Jenkins contention

(cherry picked from commit f9f5fd5f4e81828a3e0c391892e0f28751568843)
Signed-off-by: Reynold Xin <rxin@apache.org>