Correct error message when query domain id

As discussion in comments of https://review.openstack.org/132955 ,
correct error message when query domain id.

Partial-Bug: #1376213
Change-Id: Id39ee6d4acca82c908b690c748609ed1125012eb
ResourceGroup don't special-case zero count

Currently, when you specify an initial count of zero, we don't
create the nested stack.  Unfortunately this then means you can
never update it, which makes the group forever broken..

Instead, always create the stack on create, even if it's an empty
stack containing zero resources.  This allows subsequent updates
which move to a non-zero count to work as expected.

Change-Id: I494229fcf85a1c28428fa2925c060fc1f40f4f36
Closes-Bug: #1392796
RandomString physical_resource_id as id not the string

If someone choses a string length of over 255 we overflow the DB
id field causing an error, so instead use the physical name 
for the resource_id.

The actual string is already stored (encrypted) in the resource_data
so it's probably better anyway to refer to the value in one place
and just override FnGetRefId to maintain the existing interface behavior.

Change-Id: Ide8899a2aa0a9fed037835dc46225f52c291ace6
Closes-Bug: #1392359
Merge "RandomString physical_resource_id as id not the string"
Merge "Correct error message when query domain id"
Merge "ResourceGroup don't special-case zero count"