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.
11c169501e