Network interface metrics are not displayed when openstack metric resource show is executed against instance uuid

Issue

• Gnocchi doesn't lists network interface metrics when gnocchi metric show is executed against instance uuid.

  # openstack metric resource show 92898284-4a19-4355-a153-1ed455fc4b6d
  
  +-----------------------+----------------------------------------------------------------+
  | Field                 | Value                                                          |
  +-----------------------+----------------------------------------------------------------+
  | created_by_project_id | df34aa4b02da471d8c3ef5044f4c8655                               |
  | created_by_user_id    | 55ab2e71d2f84060bfed02229a1c189a                               |
  | ended_at              | None                                                           |
  | id                    | 92898284-4a19-4355-a153-1ed455fc4b6d                           |
  | metrics               | cpu.delta: e146f00e-31a7-4fd1-b473-3a8bc4ff502d                |
  |                       | cpu: 5fc4b72a-d0aa-42a1-9ae4-eafd711dafd3                      |
  |                       | cpu_util: f3a2aa30-b2c8-49ee-9227-e928474f4b47                 |
  |                       | disk.allocation: 132b7a25-4794-404b-a0d7-998644e224a5          |
  |                       | disk.capacity: bdd54238-151b-4cd9-9493-502e7bbcaef5            |
  |                       | disk.ephemeral.size: b6c3f539-9bc6-4688-9b10-b52bc066699a      |
  |                       | disk.iops: b3df8dd7-758a-4397-9467-538ab8d025bc                |
  |                       | disk.latency: 2c2c68ec-4654-46fa-bfcc-fd07785a0bb3             |
  |                       | disk.read.bytes.rate: 61cade68-e803-432b-9d35-57f0d45d5ee6     |
  |                       | disk.read.bytes: 6d4f31b9-7324-41d6-beab-cae1b4a73886          |
  |                       | disk.read.requests.rate: 15496256-05d0-439a-9b47-9302f118aeeb  |
  |                       | disk.read.requests: 4c1d1659-f294-4161-9799-31f0b57a6550       |
  |                       | disk.root.size: 3d31c79f-f794-444b-adfe-05de01cd983c           |
  |                       | disk.usage: c1ff4f31-2c54-4bfd-a5c9-f02ffbe9b32a               |
  |                       | disk.write.bytes.rate: 828ddbe0-6a9f-4cae-9a0f-ec5d3b2e68dd    |
  |                       | disk.write.bytes: a5ad0e24-7e95-4f4c-9d4e-15dfa05fc3f8         |
  |                       | disk.write.requests.rate: 9916405b-c431-4c39-92ba-35e5a7805e0c |
  |                       | disk.write.requests: 570ab46e-b56d-4dc5-89fb-afc98a18fb7b      |
  |                       | instance: 11e52a50-d75a-4f70-a0e0-b7ca65cafff5                 |
  |                       | memory.resident: f69056a1-73e9-4ad5-8ed5-ca4bf7fea010          |
  |                       | memory.usage: 3d8c2762-cc49-4671-9a6b-fc09ac54d1bc             |
  |                       | memory: 38164b4d-51b6-4f33-b35a-b66417c0425b                   |
  |                       | vcpus: fa796f7f-bb16-4eda-bcf9-df223d17b0df                    |
  | original_resource_id  | 92898284-4a19-4355-a153-1ed455fc4b6d                           |
  | project_id            | 72835d1573b44d3fae3a2464344dd159                               |
  | revision_end          | None                                                           |
  | revision_start        | 2018-10-26T09:12:44.129306+00:00                               |
  | started_at            | 2018-05-24T12:56:50.170183+00:00                               |
  | type                  | instance                                                       |
  +-----------------------+----------------------------------------------------------------+