stdlib::ensure: new fuction to cast ensure values

[b4ldr]

This PR adds a new function to cast the ensureable property to a resource

specific value. e.g.

• stdlib::ensure('present', 'service') == 'running'
• stdlib::ensure('present', 'directory') == 'directory'

This is useful when you want to pass ensure to a custom class and
ensure all the resource get the correct value e.g.

class foo(
  Enum['present', 'absent'] $ensure = 'present'
) {
  file {'/some/dir':
    ensure => stdlib::ensure($ensure, 'directory')
  }
  file {'/some/file':
    ensure => stdlib::ensure($ensure, 'file')
  }
  file {'/some/link':
    ensure => stdlib::ensure($ensure, 'link')
  }
  service {'some-service':
    ensure => stdlib::ensure($ensure, 'service')
  }
}

something similar to this was discussed in #869

[b4ldr]

The travis-ci failures seem unrelated to this change

[pmcmaw]

I firstly want to congratulate you on writing our first ever function in Puppet language for this module!

And I then want to thank you for taking the time. We always love to see community contributions and this function is pretty cool.

:-)