Travis: Perform docker login in before_install:

Author: pdhar-tibco

.travis.yml

@@ -11,6 +11,7 @@ git:
 # Do a github login using token
 before_install:
   - "echo -e \"machine github.com\n  login ${GITHUB_USER_TOKEN}\" >> ~/.netrc"
+  - "docker login -u=\"${DOCKER_USERNAME}\" -p=\"${DOCKER_PASSWORD}\" "
 
 script: 
   - touch flogo-cli.tgz
@@ -33,7 +34,6 @@ after_script:
 
 after_success:
   - "if [ \"${TRAVIS_BRANCH}\" == \"master\" ]; then
-    docker login -u=\"${DOCKER_USERNAME}\" -p=\"${DOCKER_PASSWORD}\";
     source ${TRAVIS_BUILD_DIR}/flogo-cicd/scripts/init.sh ;
     flogo::module::postbuild flogo-cli flogo-cli ;
     fi"