Support any distribution without UserData/MetaData

A template without UserData or MetaData sections should work with any
distribution, regardless of whether or not a setup script exists for
it in the Cloud Servers resource. The setup script only exists so that
the UserData and MetaData sections will configure the server.

Bug 1204650

Change-Id: Ie795ff63a5a15916c67d96782ea01d604d4768b0
Merge "Support any distribution without UserData/MetaData"