GUI-1231: VPC support for scaling group wizard and detail page

https://eucalyptus.atlassian.net/browse/GUI-1231
https://eucalyptus.atlassian.net/browse/GUI-1232
Tthe attribute "vpc_zone_identifier' needs to be a string that lists the vpc subnet IDs, separated by comma, in order for the update call (line 312) to work correctly:
self.scaling_group.update()

The method get_vpc() at line 317 is a function that is not used by the update call above, rather it processes the received scaling_group directly from boto.

The extra space ", " was removed.