Fixes https://emqx.atlassian.net/browse/EMQX-9392
The returned information does not allow to diagnose the issue (i.e.: a
connection issue due to the wrong host and port, the wrong password
failing authn). However, such information is printed to the logs.
This changes the returned error to the API so that the user is hinted
at looking at the logs for further investigation of the error.