Misc/Travis: Enable Travis in the coverity_scan branch & add coverity badge to readme

.travis.yml

@@ -18,6 +18,7 @@ branches:
   only:
     - master
     - 4.3.4
+    - coverity_scan
 
 git:
   depth: 1

README.md

@@ -1,6 +1,7 @@
 # ![logo](http://www.trinitycore.org/f/public/style_images/1_trinitycore.png) TrinityCore
 
 [![Build Status](https://travis-ci.org/TrinityCore/TrinityCore.svg?branch=master)](https://travis-ci.org/TrinityCore/TrinityCore)
+[![Coverity Scan Build Status](https://scan.coverity.com/projects/435/badge.svg)](https://scan.coverity.com/projects/435)
 
 ## Introduction