Domain assigned to instances are unique for all the OSP infrastructure, so each user cannot select its own domain

Issue

• The domain used to create the FQDN of the instances in OSP is unique for the deployment, wether it can be tuned using the parameter dns_domain of neutron.conf, it still cannot be selected per user or tenant.
• When integrating OSP with external DNS service, users cannot assign different domain to each instance (like environment (lab, test, production).