Fixes #107 ("Hanlon subnet" check fails under Tomcat)

When Hanlon is deployed under Tomcat, calls to `Facter.value(:kernel)`
return an empty string. As a result, attempts to get the list of available
interfaces, a value from a specific interface, or the output containing
the text from a single interface using Facter all return either nil or an
empty string. This commit monkey-patches the Facter::Util::IP module
(within the Hanlon::WebService::Utils module) so that the correct
values are returned when the `Facter::Util::IP.get_interfaces` or
`Facter::Util::IP.get_interface_value(interface, label)` methods
are called (even when Hanlon is deployed under Tomcat)
Small change to make call order in the attempted `ifconfig` calls consistent
(first, try `/sbin/ifconfig`, then `/usr/sbin/ifconfig`)  in the monkey-patched versions
of the `Facter::Util::IP.get_interfaces` and `Facter::Util::IP.get_single_interface_output`
methods
Ensure that the `output` value from the `get_single_interface_output` method is returned.  Ironically enough, prior to this change if the first attempt (using the `/sbin/ifconfig` command) succeeded the method returned a nil...
Merge pull request #108 from tjmcs/tb/fix-hanlon-subnet-test

Fixes #107 ("Hanlon subnet" check fails under Tomcat)