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.
While declaring `emqx_conf` as an application dependency of
`emqx_resource` worked for releases, it messed up the startup
relationship during tests. Since only removing `emqx_conf` from the
`applications` key in `emqx_resource` breaks the list of apps that
need to be rebooted on config changes (since `emqx_conf` is not on any
apps dependencies list, it was not being added to the final
topologically sorted list), we now always add it as a vertex to ensure
its presence there. This (apparently) makes the rebar3 release, the
mix release and test runs behave normally.
This commit enables a minimal working build of EMQX release using
Mix. However, to properly start the release, several configuration
steps are still missing. A `mix_release.sh` script does a few hacks
to get the release built with Mix to start properly, by first assuming
that `make emqx` has been run prior to the release, ran once to
generate the `app.*.config` files, and then it copies that and some
other files to the expected places.
Also, `emqx_telemetry` hangs the start procedure because it thinks
it's in an official release and tries to make a request. We disable
it temporarily via config just to get a working build for now.
