Skip sonarqube analysis on pull request builds

Sonarqube requires the credentials for sonarqube.io when analysing the
project. Since these are stored in encrypted env variables on Travis
they are not available on pull request builds which causes the build to
fail.

Author: cboehme

.travis.yml

@@ -16,7 +16,7 @@ before_install:
 
 script:
   - ./gradlew check
-  - ./gradlew sonarqube
+  - ./travis/sonarqube.sh
 
 after_success:
   - ./travis/publish.sh

travis/sonarqube.sh

@@ -0,0 +1,15 @@
+#!/usr/bin/env bash
+
+function main {
+    require_no_pull_request
+    ./gradlew sonarqube
+}
+
+function require_no_pull_request {
+    if [ -v TRAVIS_PULL_REQUEST -a "$TRAVIS_PULL_REQUEST" != "false" ]; then
+        echo "Building pull request. Skipping sonarqube analysis"
+        exit 0
+    fi
+}
+
+main