Improve replicator error reporting
Previously many HTTP requests failed noisily with `function_clause` errors.
Expect some of those failures and handle them better. There are mainly 3 types
of improvements:
1) Error messages are shorter. Instead of `function_clause` with a cryptic
internal fun names, return a simple marker like `bulk_docs_failed`
2) Include the error body if it was returned. HTTP failures besides the error
code may contain useful information in the body to help debug the failure.
3) Do not log or include the stack trace in the message. The error names are
enough to identify the place were they are generated so avoid spamming the
user and the logs with them. This is done by using `{shutdown, Error}` tuples
to bubble up the error the replication scheduler.
There is a small but related cleanup of removing source and target monitors
since we'd want to handle those error better however those errors are never
triggered since we removed local replication endpoints recently.
Fixes: https://github.com/apache/couchdb/issues/2413
5 files changed
