enabled to use upper case letters and region-name for hp_avl_zone option...

hi,

I confused about knife[:hp_avl_zone] option of knife.rb because README.md includes these lines.

<pre>
knife[:hp_avl_zone]   = "Your HP Cloud Availability Zone" (optional, default is 'region-a.geo-1', the other option is 'region-b.geo-1').
</pre>

So I could not use such 'region-a.geo-1' for hp_avl_zone setting. 
And I am fog user, too. so I think that we should use region-name (such as 'region-a.geo-1') for knife[:hp_avl_zone] option.

Thanks from Sunny Tokyo. :dash: