Add Travis dispatching script to run test suite

Use a dispatch script to direct Travis to either run a Salt highstate
for most nodes, or the test script for the test node.

This reduces the amount of project-specific configuration in .travis.yml
and moves it into a separate file.

.travis.yml

@@ -20,23 +20,16 @@ matrix:
       os: linux
       sudo: required
       dist: trusty
+    - env: SALT_NODE_ID=test # Not a Salt node, runs test suite instead
+      os: linux
+      sudo: required
+      dist: trusty
+      language: python
+      python: 3.5
   allow_failures:
     - env: SALT_NODE_ID=servo-linux-cross1
 
-before_install:
-  - .travis/install_salt.sh -F -c .travis -- "${TRAVIS_OS_NAME}"
-
-install:
-  - .travis/setup_salt_roots.sh
-
-  # For debugging, check the grains reported by the Travis builder
-  - sudo salt-call --id="${SALT_NODE_ID}" grains.items
-
-script:
-  # Minimally validate YAML and Jinja at a basic level
-  - sudo salt-call --id="${SALT_NODE_ID}" --retcode-passthrough state.show_highstate
-  # Full on installation test
-  - sudo salt-call --id="${SALT_NODE_ID}" --retcode-passthrough --log-level=warning state.highstate
+script: .travis/dispatch.sh
 
 notifications:
   webhooks: http://build.servo.org:54856/travis

.travis/dispatch.sh

@@ -0,0 +1,23 @@
+#!/usr/bin/env sh
+
+set -o errexit
+set -o nounset
+
+if [ "${SALT_NODE_ID}" = "test" ]; then
+    # Using .travis.yml to specify Python 3.5 to be preinstalled, just to check
+    printf "Using $(python3 --version) at $(which python3)\n"
+
+    # Run test suite separately for parallelism
+    ./test.py
+else
+    .travis/install_salt.sh -F -c .travis -- "${TRAVIS_OS_NAME}"
+    .travis/setup_salt_roots.sh
+
+    # For debugging, check the grains reported by the Travis builder
+    sudo salt-call --id="${SALT_NODE_ID}" grains.items
+
+    # Minimally validate YAML and Jinja at a basic level
+    sudo salt-call --id="${SALT_NODE_ID}" --retcode-passthrough state.show_highstate
+    # Full on installation test
+    sudo salt-call --id="${SALT_NODE_ID}" --retcode-passthrough --log-level=warning state.highstate
+fi