CBG-4407 synchronously stop xdcr from CBS

[torcolvin]

This increases the time of the XDCR package by about 20% on my computer.

Greps the goxdcr.log file for the magic string. Tested on local Linux, docker linux, cbdinocluster multi node setup (where this is not supported). I can not successfully run Couchbase Server on Mac for reasons that are not related to this ticket and I am reluctant to sink more time into debugging right now.

This will require setting export SG_TEST_COUCHBASE_SERVER_DOCKER_NAME="couchbase" if couchbase server docker is used, but the error message should say that.

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

• GSI=true,xattrs=true https://jenkins.sgwdev.com/job/SyncGateway-Integration/2887/