travis: use homebrew addon for MacOSX

Rather than poking homebrew manually we can specify the packages
needed via the homebrew addon. These are only installed on MacOS based
builds.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>

.travis.yml

@@ -42,6 +42,12 @@ addons:
       - sparse
       - uuid-dev
       - gcovr
+  homebrew:
+    packages:
+      - libffi
+      - gettext
+      - glib
+      - pixman
 
 
 # The channel name "irc.oftc.net#qemu" is encrypted against qemu/qemu
@@ -68,9 +74,6 @@ git:
   submodules: false
 
 
-before_install:
-  - if [ "$TRAVIS_OS_NAME" == "osx" ]; then brew update ; fi
-  - if [ "$TRAVIS_OS_NAME" == "osx" ]; then brew install libffi gettext glib pixman ; fi
 before_script:
   - mkdir -p ${BUILD_DIR} && cd ${BUILD_DIR}
   - ${SRC_DIR}/configure ${CONFIG} || { cat config.log && exit 1; }