Fix aggregated domain metrics test fixture

[mikelorant]

The aggregated metrics for the domain test had the host incorrectly set.

Fixed the indentation to be consistent with the other fixtures.

[mikelorant]

@leklund While implementing the tests for the domain metrics, I found that the domain was marked as an origin (likely copied from the origin metrics). This caused the tests to fail:

 - 	`testspace_domain_bereq_body_bytes_total{datacenter="aggregate",domain="testhost",service_id="my-service-id",service_name="my-service-name"}`:                         16,
 + 	`testspace_domain_bereq_body_bytes_total{datacenter="aggregate",domain="testorigin",service_id="my-service-id",service_name="my-service-name"}`:                       16,

Since this is unrelated to the aggregated metrics, felt it was better to put this up as a separate pull request.