Add tox-nodejs-npm base job for python and javascript

Sometimes projects are multi-language. Specifically, sometimes they need
to run both javascript and python toolchains. Support this by making a
tox-nodejs-npm job which installs both toolchains, then runs the npm
command followed by the tox command.

Most people won't need/want this, but it should make at least some folks
happy.

Change-Id: Iaedd680a548c6e8159693b7a79cd8676e805aa1f

playbooks/tox/npm.yaml

@@ -0,0 +1,5 @@
+- hosts: all
+  roles:
+    - revoke-sudo
+    - npm
+    - tox

zuul.yaml

@@ -137,6 +137,66 @@
     vars:
       tox_envlist: bashate
 
+- job:
+    name: tox-nodejs-npm
+    parent: tox
+    description: |
+      Run tests using tox but with the javascript toolchain installed
+      and available as well. A combination of the tox and nodejs-npm
+      jobs. By default will run npm before running the tox environment listed.
+
+      Responds to these variables:
+
+      .. zuul:jobvar:: tox_envlist
+
+         Use the specified tox environments (``ALL`` selects all).
+
+      .. zuul:jobvar:: tox_environment
+
+         List of user defined environmental variables to pass to bash
+         shell.
+
+      .. zuul:jobvar:: tox_extra_args
+
+         String containing extra arguments to append to the tox command line.
+
+      .. zuul:jobvar: tox_constraints_file
+
+         Path to a pip constraints file. Will be provided to tox in the
+         UPPER_CONSTRAINTS_FILE environment variable if it exists.
+
+      .. zuul:jobvar: tox_install_siblings
+         :default: true
+
+         Override tox requirements that have corresponding zuul git repos
+         on the node by installing the git versions into the tox virtualenv.
+
+      .. zuul:jobvar:: npm_command
+         :default: build
+
+         Command to pass to npm.
+
+      .. zuul:jobvar:: node_version
+         :default: 6
+
+         The version of Node to use.
+
+
+      .. zuul:jobvar: javascript_content_dir
+         :default: dist
+
+         Directory, relative to zuul_work_dir, holding build content.
+
+      .. zuul:jobvar: zuul_work_dir
+         :default: {{ zuul.project.src_dir }}
+
+         Path to operate in.
+    pre-run: playbooks/javascript/pre.yaml
+    run: playbooks/tox/npm.yaml
+    post-run: playbooks/javascript/post.yaml
+    vars:
+      npm_command: build
+
 - job:
     name: build-python-release
     description: |