Microversion 2.94: FQDN in hostname

Extend microversion 2.90 to allow FQDNs in the hostname parameter.
Multi-create with --hostname continues to be refused, returning error
400 to the user. This simplifies the code by not needing to handle any
sort of suffix or prefix mangling of the FQDN to handle multiple
instances. No other changes are made - not Neutron integration,
metadata API changes (the FQDN will appear as-is in places where the
hostname currently appears), etc.

Change-Id: I47e397dc6da8263762479cc8ae4f8777a6d9d811
Implements: bp/fqdn-in-hostname

api-ref/source/parameters.yaml

@@ -6382,6 +6382,9 @@ server_hostname_req:
   description: |
     The hostname to configure for the instance in the metadata service.
 
+    Starting with microversion 2.94, this can be a Fully Qualified Domain Name
+    (FQDN) of up to 255 characters in length.
+
     .. note::
 
         This information is published via the metadata service and requires