Refactor jenkins_job with idempotency
Convert jenkins_plugin to an HWRP
Remove jenkins_cli
Document jenkins_command HWRP
Add `jenkins_command` test. Make executor load first.

This commit adds a simple Test Kitchen test for `jenkins_command` as well as
prefixes the `libraries/_exector.rb` file with an underscore to ensure it's
loaded before all other libraries. This also helps visually separate which
libraries are HWRPs and which are "helpers".
Improve documentation on jenkins_command
Support authentication and proxy configuration via node attributes
Cache the contents of the current plugin
Add `jenkins_user` resource

This commit also introduces changes to the `.kitchen.yml` and a shared
`spec_helper.rb` and data directory for testing the Jenkins user.
Add `jenkins_command` test suite and fixtures
Add `jenkins_job` test suite and fixtures
Remove old CLI integration tests
Only download the remote file if it doesn't already exist

This may seem a bit weird, but instead of adding a `remote_file` reosurce
to the resource collection on each run, we are using a simple File.exists?
check to guard the execution. Since the executor is _heavily_ used, the
`remote_file` significantly clogs up the debugging output and isn't an ideal
user experience.

This behavior is exactly the same as `:create_if_missing`, but the resource
is not added to the collection if it already exists.
Add `jenkins_plugin` test suite and fixtures
Don't pollute the global namespace

Serverspec pollutes the global RSpec namespace like a bad boy. Using common
idioms like `installed?` or `exists?` is risky. Thus, this commit makes
the matchers more semantic and less likely to collide.
Remove @sethvargo-specific things from the .kitchen.yml
Update to Test Kitchen 1.1.1
Make the test instances beefier..cause JAVA.
Ensure the Jenkins API/UI is accessible from the host
Make Ubuntu 12.04 (latest LTS) is default test platform