GUI-1294, GUI-1310 Disable the VPC subnet select options if they are in the same zone as th...

...e selected VPC subnets in the scaling group wizard and detail page.
https://eucalyptus.atlassian.net/browse/GUI-1294
https://eucalyptus.atlassian.net/browse/GUI-1310
@kyolee310 Consider using str.format() here, which would make this line a bit cleaner…

`subnet_string = '{0} ({1}) | {2}'.format(vpc.cidr_block, vpc.id, vpc.availability_zone)`