config: fix test-only failures in UI handler setup (#11571)
config: fix test-only failures in UI handler setup (#11571)

The `TestHTTPServer_Limits_Error` test never starts the agent so it
had an incomplete configuration, which caused panics in the test. Fix
the configuration.

The PR #11555 had a branch name like `f-ui-*` which caused CI to skip
the unit tests over the HTTP handler setup, so this wasn't caught in
PR review.
hashicorp/nomad,hashicorp/nomad,hashicorp/nomad,hashicorp/nomad,hashicorp/nomad,hashicorp/nomad