Add jenkins::api_user defined type

Wrapper for creating Jenkins user accounts with preset API tokens. This will
allow us to decouple slave authenication from LDAP/oAuth and preseed the
credentials for all environments.
Align hash rockets in jenkins::api_user specs.
puppetdoc to cover use of title for username
Add a warning to api_user descriptions

Make it apparent to humans that these user accounts have been created
automagically and cannot be modified from the Jenkins UI.
Merge pull request #1 from alphagov/create_api_user

Add jenkins::api_user defined type