Manage options

[kenyon]

• More flexibility in configuration
• fixtures: update puppet-systemd URL to voxpupuli
• convert Debian options file template to EPP
• RedHat: add default tftp::options
• config: add unit tests for tftp::options

This PR takes #115 and makes small changes to enable management of tftpd options. See also #153 and #141, but my PR is intended to be small enough to review easily so that we can merge it, then add the other features of those other PRs.

[kenyon]

Not sure what we need to do to bring in the puppet method in acceptance testing.

An error occurred while loading ./spec/acceptance/tftp_port_spec.rb.
Failure/Error: on hosts, puppet('resource', 'package', 'tftp', 'ensure=installed')
NoMethodError:
  undefined method `puppet' for RSpec::ExampleGroups::TftpWithDefaultParameters::EnsureTftpClientIsInstalled:Class
  
# ./spec/acceptance/tftp_port_spec.rb:42:in `block (2 levels) in <top (required)>'
# ./spec/acceptance/tftp_port_spec.rb:41:in `block in <top (required)>'
# ./spec/acceptance/tftp_port_spec.rb:3:in `<top (required)>'