Use Regex against Facts for setting default hostgroup

This change would allow the use of a regex against any given fact rather that just the hostname of the machine. 

The first match found  as listed in the config would be applied to the machine. As ruby 1.9.x retains the order of a hash read from config, this should be a reliable way of establishing the priority.

Eventually I would like to perhaps do compound comparisons (If factA = regex and FactB = regex), but this seems like a good start.

Open to any and all suggestions!
We also need some tests for the multi-regex support. These hashes spring to mind:
```
invalid keys ignored: { "First Group" => { 'nosuchfact' => '.*', 'hostname' => '.*' }}
unmatched values ignored: { "First Group" => { 'hostname' => 'nosuchname', 'osfamily' => '.*' }}
```