Prior to this change, when EMQX daemon mode failed to start
it's not quite easy for users to understand what went wrong.
All the know is the node did not start in time
and then instructed to boot the node in 'console' mode wishing
for some logs.
However, the node might actuay be running, causing 'console' mode
to fail with a different reason.
With this change, after a filure of daemon mode boot,
we issue a diagnosis.
1. if node can not be found from ps -ef, instruct the user
to find information in erlang.log.N
2. if the node is found running, but not responding to pings
instruct the user to check if the node name is
resolvable and reachable
3. if the node is responding to pings but emqx app is not
running, then it's likely a bug. so the user is advised
to report a github issue.
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