ignore tag selection, introduced ignore_tag parameter for plugin

setting ignore_tag <used_tag_value>, and tagging host in amazon with use=<used_tag_value>, will cause this module to evict host from listing, useful when some machines are not used 24/7 or like our case we don't care for demo and devel servers
Merge pull request #2 from andrus7k/patch-1

ignore tag selection, introduced ignore_tag parameter for plugin