use generic ip_address resource

[kaminek]

The current implementation only allows floating IP addresses as a resource resource_floating_ip_address, we want to have a more generic IP address where the floating is an optional param.
Following the API
This can allows more attributes to be set like ptr_record for an IP address (#60)

[kaminek]

The current API don't allow creation of stand alone IP addresses, a server UUID is required on creation. Thus this generic ip_address resource if implemented will useless atm.