Pre-emptive Ubuntu 14.04 / Ruby 1.9.3 fixes

Two fixes required in order for this module to work under Ubuntu 14.04 (which ships with Ruby 1.9.3):
* The String#each method has been deprecated; each_line needs to be used in this case instead;
* Passing dnsmasters directly (as an array returned from a Hiera lookup) results in Ruby inserting [] into dhcpd.zones causing dhcpd to barf on startup.  This has been changed to specify an element from that returned array instead.

Tested on 12.04 and 14.04.