test: fix a random failure with metric listing
test: fix a random failure with metric listing

The test
`gabbi.suitemaker.test_gabbi_prefix_resource_request_metrics_from_one_of_the_instances.test_request'
can fail in random cases with:

  AssertionError: Unable to match $[0].resource_id as 85c44741-cc60-4033-804e-2d3098c7d2e9, got d13982cb-4cce-4f84-a96e-7581be1e599c

because there are 2 resources with disk.util metrics and the list is not
be ordered.

Change-Id: I233c83028cb7295d81b00b2181eb23b8ab96ce97

gnocchixyz/gnocchi,gnocchixyz/gnocchi,sileht/gnocchi,leandroreox/gnocchi,sileht/gnocchi,leandroreox/gnocchi