travis: Add macports-based OSX script

.travis.yml

@@ -11,4 +11,15 @@ matrix:
             - libavahi-compat-libdnssd-dev
       script: sh -x ./clean_build.sh
 
+    - os: osx
+      osx_image: xcode9
+      script:
+        - export COLUMNS=80
+        - curl -LO https://raw.githubusercontent.com/GiovanniBussi/macports-ci/master/macports-ci
+        - chmod +x ./macports-ci
+        - ./macports-ci install
+        - PATH="$PATH:/opt/local/bin"
+        - sudo port -N install qt5-qtbase openssl
+        - sh -x ./clean_build.sh
+
 install: true