Subnet sharing feature groups public and private subnets into one share.

[dogfish182]

If both public and private sharing is enabled, the sharing module will group both of these types of subnets into 1 share. This is not highly desirable, because for a lot of legacy workloads, it would be useful to ONLY share private subnets (and vice versa).

Logging this issue to track it as I will likely have a requirement to seperate these in early october.