Couchdb Metrics Receiver

[JonathanWamsley]

Add support for Couchdb Metrics.

NOTE: SLES is not supported natively by Couchdb.

[JonathanWamsley]

The ops agent integration test had an unrelated failure on TestLoggingAgentCrashRestart failed

[JonathanWamsley]

The third party apps integration test passed for couchdb but failed an unrelated test on tomcat

[quentinmit]

What happens if you use the default configuration instead?

[JonathanWamsley]

see above

[qingling128]

Overall LGTM modulo the remaining 3 open threads are addressed, and the integration tests are fixed (Probably some minor issue triggered by the suggested renaming):

[qingling128]

LGTM.

Needs rebasing before merging. If the conflicts are limited to the golden files, we can skip running the integration tests again, as they passed already.

[qingling128]

Note for Jimmy, the full documentation can be found in https://github.com/GoogleCloudPlatform/ops-agent/blob/90d604b692cffb9cf388948e586cf5e2a894b2d0/docs/couchdb.md

Note for future reference: Currently we are trying to automate the documentation generation for https://cloud.google.com/stackdriver/docs/solutions/agents/ops-agent/third-party. Before that is completed, the workflow is:

1. ObserveIQ contributes documentation (in the format of https://github.com/GoogleCloudPlatform/ops-agent/blob/90d604b692cffb9cf388948e586cf5e2a894b2d0/docs/couchdb.md) as docs/{APP_NAME}.md files.
2. Jimmy to take these markdown and turn them into the expected format for https://cloud.google.com/stackdriver/docs/solutions/agents/ops-agent/third-party
3. We then comes back to GitHub to delete the install instructions to avoid maintaining two copies for the long term after https://cloud.google.com/stackdriver/docs/solutions/agents/ops-agent/third-party/{APP_NAME} is published.