Start mosquitto daemon accordingly to what is used on each support Travis CI OS

Signed-off-by: Otavio Rodolfo Piske <opiske@redhat.com>

.travis.yml

@@ -10,8 +10,8 @@ os:
   - osx
 
 before_install:
-  - if [[ "$TRAVIS_OS_NAME" == "osx" ]]; then brew install openssl mosquitto ; fi
-  - mosquitto -d
+  - if [[ "$TRAVIS_OS_NAME" == "osx" ]]; then brew install openssl mosquitto ; brew services start mosquitto ; fi
+  - if [[ "$TRAVIS_OS_NAME" == "linux" ]]; then mosquitto -d ; fi 
 
 script:
   - mkdir build.paho ; cd build.paho; cmake -DPAHO_WITH_SSL=TRUE -DPAHO_BUILD_DOCUMENTATION=FALSE -DPAHO_BUILD_SAMPLES=TRUE .. ; make ; ctest -VV