CI: Dockerized language port tests (#5066)

This runs a script in TravisCI that executes a bunch of small Docker image
scripts to test the language ports in isolated environments. This allows us to
test multiple language versions with little additional complexity.

Covers:

+ Java OpenJDK 10.0.2
+ Java OpenJDK 11.0.1
+ Node 10.13.0
+ Node 11.2.0
+ Python CPython 2.7.15
+ Python CPython 3.7.1
+ Rust 1.30.1

.travis.yml

@@ -57,6 +57,17 @@ matrix:
     #      skip_cleanup: true
     #      on:
     #        branch: master
+    - language: cpp
+      os:
+        - linux
+
+      addons:
+        apt:
+          packages:
+            - docker-ce
+      script:
+        - bash .travis/build-and-run-docker-test-containers.sh
+
     - language: cpp
       os:
         - linux