travis: Rewrite the CI config to use platform matrix

.travis.yml

@@ -1,10 +1,14 @@
 language: cpp
-before_install:
-- sudo apt-get update -qq
-- sudo apt-get install -qq libxtst-dev
-- sudo apt-get install -qq qtdeclarative5-dev
-- sudo apt-get install -qq libavahi-compat-libdnssd-dev
-script: sh -x ./clean_build.sh
-# skip install phase since we have a customized install package
-# creation tool for each supported platform
+
+matrix:
+  include:
+    - os: linux
+      addons:
+        apt:
+          packages:
+            - libxtst-dev
+            - qtdeclarative5-dev
+            - libavahi-compat-libdnssd-dev
+      script: sh -x ./clean_build.sh
+
 install: true