New test suite for the DHCP API

This is built around the ISC DHCPD provider, the goal is testing the API layer.
Run the DHCP tests in alphabetical order
Move dhcp configs into test/fixtures/dhcp/
Test for ISC DHCP included files
Clean up the params input to the DHCP::Server.addRecord method

This fixes the ability to match and ignore pre-existing identical DHCP records.
Avoid nested arrays and extra array copies in the ISC DHCP config parser
Common code for manage_subnet? in ISC and Native MS