When creating/provisioning a domain, handle Error case when a service already exists in cloud.gov

[davemcorwin]

User Story

As an admin, I'd like a more informative error message when a domain service already exists in cloud.gov, or other failure cases.

Acceptance Criteria

• [ ] better handle failure cases when provisioning domains
• [ ] Change made live via deploy federalist app.

After evaluating, edit this part:

Level of effort - <low/medium/high>

Implementation outline (if higher than "low" effort):

• [ ] <TODO>