Salt couchdb returner does not support couchdb >= 3

Description

In CouchDB 3, admin party mode was
removed,
requiring a username and password. Currently, Salt's couchdb returner does
not require or even allow a username/password. This should be fixed.

Setup

Launch a docker container from the official couchdb image:

docker run --rm -it -e COUCHDB_USER=fnord -e COUCHDB_PASSWORD=fnord -p 5984:5984 --name loose_change couchdb

Now configure your minion to use couchdb:

docker run --rm -it --link loose_change:loose_change saltstack/salt:3004
cat <<EOF> /etc/salt/minion
couchdb.url: http://loose_change:5984
EOF
salt-call --local test.version --return=couchdb

You'll see an error message:

[ERROR   ] Unable to create database 'salt'
[ERROR   ] Nothing logged! Lost data.

We'll need to change up the returner to actually support couchdb 3>=

Start with Salt's CouchDB returner and reproduce the failure using the official CouchDB Docker image with COUCHDB_USER and COUCHDB_PASSWORD, then the shown minion configuration and salt-call command. Done means the returner accepts credentials and successfully creates or uses the salt database on CouchDB 3 or newer without the reported error.