knife ssh should accept -a ec2.public_hostname

fqdn of ec2 nodes is no good because its internal, so we want the ec2.public_hostname attribute.

% knife ssh 'role:production' 'uptime' -a ec2.public_hostname
/Library/Ruby/Gems/1.8/gems/net-ssh-multi-1.0.1/lib/net/ssh/multi/server.rb:47:in `initialize': undefined method `match' for nil:NilClass (NoMethodError)
from /Library/Ruby/Gems/1.8/gems/net-ssh-multi-1.0.1/lib/net/ssh/multi/session.rb:279:in `new'
from /Library/Ruby/Gems/1.8/gems/net-ssh-multi-1.0.1/lib/net/ssh/multi/session.rb:279:in `use'
from /Library/Ruby/Gems/1.8/gems/net-ssh-multi-1.0.1/lib/net/ssh/multi/session.rb:278:in `map'
from /Library/Ruby/Gems/1.8/gems/net-ssh-multi-1.0.1/lib/net/ssh/multi/session.rb:278:in `use'
from /Library/Ruby/Gems/1.8/gems/chef-0.8.0/lib/chef/knife/ssh.rb:52:in `configure_session'
from /Library/Ruby/Gems/1.8/gems/chef-0.8.0/lib/chef/search/query.rb:46:in `call'
from /Library/Ruby/Gems/1.8/gems/chef-0.8.0/lib/chef/search/query.rb:46:in `search'
from /Library/Ruby/Gems/1.8/gems/chef-0.8.0/lib/chef/search/query.rb:46:in `each'
from /Library/Ruby/Gems/1.8/gems/chef-0.8.0/lib/chef/search/query.rb:46:in `search'
from /Library/Ruby/Gems/1.8/gems/chef-0.8.0/lib/chef/knife/ssh.rb:51:in `configure_session'
from /Library/Ruby/Gems/1.8/gems/chef-0.8.0/lib/chef/knife/ssh.rb:155:in `run'
from /Library/Ruby/Gems/1.8/gems/chef-0.8.0/lib/chef/application/knife.rb:110:in `run'
from /Library/Ruby/Gems/1.8/gems/chef-0.8.0/bin/knife:26
from /usr/bin/knife:19:in `load'
from /usr/bin/knife:19