Docker builds on Travis (#343)

* attempt to build on travis using docker

* run tests in foreground

* add examples to travis tests

* test from current checkout

* attempt to fix docker version issues

* try build with xenial

* attempt docker upgrade

* avoid hang on configuration files

* matrix osx and linux w/ docker

* restore non-test docker builds

* fix typo

* tuning and cleanup

* add missing file

* comment cleanup

docker/examples/Dockerfile

@@ -1,3 +1,6 @@
+# Bulding on top of deploy image, this Dockerfile adds libraries needed
+# for running examples.
+
 FROM amplab/ray:deploy
 
 # Tensorflow