[SPARK-4686] Link to allowed master URLs is broken

The link points to the old scala programming guide; it should point to the submitting applications page.

This should be backported to 1.1.2 (it's been broken as of 1.0).

Author: Kay Ousterhout <kayousterhout@gmail.com>

Closes #3542 from kayousterhout/SPARK-4686 and squashes the following commits:

a8fc43b [Kay Ousterhout] [SPARK-4686] Link to allowed master URLs is broken