Gui 1162 UX review for adding VPC support on the instance launch and launch config wizards

https://eucalyptus.atlassian.net/browse/GUI-1162
https://eucalyptus.atlassian.net/browse/GUI-1228
https://eucalyptus.atlassian.net/browse/GUI-1229
I would change this line to `self.vpc_network.choices = self.vpc_choices_manager.vpc_networks()` , and there's no need for the get_vpc_network_choices() method in this class.  Same for the vpc_subnet choices