travis: improve build process and expand build matrix

Make a build heriarchy to reduce images size.
Add Android Things builds to build matrix.
Drop gcc-4 builds, use gcc-5 and gcc-6 instead.
Add SonarQube static analysis scans.

Signed-off-by: Nicolas Oliver <dario.n.oliver@intel.com>

docker/Dockerfile.node

@@ -0,0 +1,17 @@
+FROM upm-base
+
+WORKDIR /opt
+
+# Node.js Build Dependencies
+RUN wget -q -O - https://raw.githubusercontent.com/creationix/nvm/v0.33.2/install.sh | bash
+ENV NVM_DIR /root/.nvm
+ARG NODE_VERSION
+RUN . $NVM_DIR/nvm.sh && nvm install $NODE_VERSION && nvm use $NODE_VERSION && \
+    npm install -g node-gyp && node-gyp install
+ENV PATH $NVM_DIR/versions/node/$NODE_VERSION/bin:$PATH
+
+# Set Workdir
+WORKDIR $UPM_SRC_DIR
+
+CMD bash
+