Allow host declaration without IP.

[mergwyn]

Pull Request (PR) description

I often use dhcp to allocate hostnames or to distribute other options (eg routers) where I don't care about the IP address. I tried similar code to the above, but (using hiera) I received a message when I did not include an IP address:

Evaluation Error: Error while evaluating a Resource Statement, Dhcp::Host[LGwebOSTV]: expects a value for parameter 'ip' (file: /etc/puppetlabs/code/environments/production/modules/dhcp/manifests/init.pp, line: 289)

I have worked around this by setting the IP address to 0.0.0.0 and then ignoring it in the template but this seems like a kludge!

This Pull Request (PR) fixes the following issues

Fixes #106

[ekohl]

It'd be better not to abuse some IP but rather make the value optional. This means changing the type to Optional[Stdlib::Compat::Ip_address] $ip = undef and changing the template as well.

[mergwyn]

Thanks for the advice. Would you also like me to squash the commits?

[bastelfreak]

@mergwyn can you please rebase and squash afterwards?

[mergwyn]

rebase and squash completed - please let me know if you need anything else.