Add `ONOS` to dictionary and fix usage in text blocks

Change-Id: I9eabdacfcff34c8e730c0148e1e6ce078cff796a
diff --git a/advanced/connectivity/external-connectivity.rst b/advanced/connectivity/external-connectivity.rst
index c8b1612..618ddf3 100644
--- a/advanced/connectivity/external-connectivity.rst
+++ b/advanced/connectivity/external-connectivity.rst
@@ -187,7 +187,7 @@
     fpm connection ip 10.6.0.1 port 2620
     !
 
-The FPM connection IP address is the IP address of **one of the onos cluster
+The FPM connection IP address is the IP address of **one of the ONOS cluster
 instances** - does not matter which one.  If you have other configuration that
 needs to go in ``zebra.conf`` you should add that here as well.