Add a node and npm package.json script for running java unit tests. Include them in the top-level npm test script. Run java unit tests in travis. Small refactor in gradlebuilder to support building gradle wrapper more easily. Don't explicitly build gradlew on appveyor CI as now npm test will do it for you.

.travis.yml

@@ -2,17 +2,25 @@ language: android
 sudo: false
 jdk:
     - oraclejdk8
+env:
+    global:
+      - ANDROID_TOOLS=${ANDROID_HOME}/tools
 before_install:
     - nvm install 6
+    # ensure at least gradle 3.3 is in place.
+    - wget http://services.gradle.org/distributions/gradle-3.3-bin.zip
+    - unzip gradle-3.3-bin.zip
+    - export GRADLE_HOME=$PWD/gradle-3.3
+    - export PATH=${GRADLE_HOME}/bin:${ANDROID_HOME}:${ANDROID_HOME}/emulator:${ANDROID_TOOLS}:${ANDROID_TOOLS}/bin:${ANDROID_HOME}/platform-tools:$PATH
     - node --version
     - gradle --version
-install:
-    - npm install
-    - npm install -g codecov
     - echo y | android --silent update sdk --no-ui --all --filter platform-tools,tools,build-tools-26.0.0,android-26,android-25,extra-google-m2repository,extra-android-m2repository
 android:
     components:
       - tools
+install:
+    - npm install
+    - npm install -g codecov
 script:
     - npm test
     - npm run cover