Log around config.FromConnStr to diagnose slow DNS SRV resolution

[bbrks]

config.FromConnStr performs SRV DNS lookups, which under some circumstances can cause slow startup times for Sync Gateway.

Log around this function to diganose and log at warning when it takes longer than 10 seconds.

Pre-review checklist

• Removed debug logging (fmt.Print, log.Print, ...)
• Logging sensitive data? Make sure it's tagged (e.g. base.UD(docID), base.MD(dbName))
• Updated relevant information in the API specifications (such as endpoint descriptions, schemas, ...) in docs/api

Integration Tests

• n/a

[torcolvin]

I think having slow DNS is relatively common.

But we actually do this in many places, usually at startup or DB startup:

sync_gateway/base/dcp_client.go

Line 323 in 5c7673e

connStrError := agentConfig.FromConnStr(connStr)

And anywhere a cluster connection is established (bootstrap) https://github.com/couchbase/gocb/blob/da582ed180ca768052410105b5e4d4394f80e674/client.go#L105

I think having any logging for this is fine, but it will not be comprehensive.

[torcolvin]

I

Suggested change

	// fromConnStrWarningThreshold determines the amount of time it should take before we warn about parsing a connstr (mostly for DNS SRV resolution)
	// fromConnStrWarningThreshold determines the amount of time it should take before we warn about parsing a connstr (mostly for DNS resolution)

I think there's other DNS resolution and the call happens to check if SRV records are there but it can do other things.

[torcolvin]

I don't think you need to address the comments, I think this would be helpful enough for users and it's not worth putting more time in it.

[bbrks]

Didn't see the other method used as it was on a different type - a text search instead of AST search found it :)