Install Guide: Fix Typos in Neutron Controller

Similiarly to the previous two bugs, this commit fixes
general typos in the controller node section of the Neutron
documentation.

This is the fourth commit in the series

Change-Id: I90616f3ca493ba86c76ca7976d2e70cbb9a6905d
Fixes: bug #1243237
(cherry picked from commit 22397bf447d61a800eed35819f2836cd0fbb02b9)