fixing multiselect issues for security groups

patched jquery.multi-select so that 'refresh' method would now refresh the select box
fixed multiselect form submission and initial loading issues
moved vpc_id from generic host object to a helper function
vpc_security_group_hash and subnet_vpc_hash added as 'data' attributes on select_f in _ec2.html.erb, they are now accessible without needing to export as JSON in this :onchange attribute
rewrote security_groups method to make it cleaner
cleaned up some test code