Allow appsody apps to use socket.io

[sam-github]

Instead of fighting over ownership of the http request event, expose the
dashboard on the user-provided express app.

server.js is modelled after the one from the appsody nodejs-express
stack, stripped down to a minimal reproduction of the chat application
failing.

Compare to:

https://github.com/appsody/stacks/blob/dc03bec53c0bfa5/incubator/nodejs-express/image/project/server.js

-- test: chat example using pre-installed socket.io

It doesn't have to use the same socket.io version as the dashboard, but
doing so allows it to use the appmetrics-dash/node_modules, instead of
having to do a `cd test/apps/chat-example; npm i` as a pre-test step.

--

test: chat-example from socket.io

From:
- https://github.com/socketio/chat-example/tree/e2530b23ffc9c17c3a1a3

The first commits add the chat example from socket.io, and show that it can work with appmetrics-dashboard by avoiding .attach() and using .monitor().

Trying that approach with the nodejs-express stack in appsody failed, so the next commits add a reproduction of the appsody failure modelled after its server.js, and modify the monitor() API to use the root express app rather than attempting to replace the http 'request' event listener.

[sam-github]

Sorry, @tobespc, I fixed the example apps and repushed.

[codecov-io]

Codecov Report

Merging #184 into master will increase coverage by 21.81%. The diff coverage is 92.53%.

@@             Coverage Diff             @@
##           master     #184       +/-   ##
===========================================
+ Coverage   64.42%   86.23%   +21.81%     
===========================================
  Files           4        4               
  Lines         416      356       -60     
===========================================
+ Hits          268      307       +39     
+ Misses        148       49       -99

Impacted Files	Coverage Δ
lib/appmetrics-dash.js	92.14% <92.53%> (+31.22%)	:arrow_up:

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[sam-github]

@tobespc Tried to make codebeat happy, I assume its a prereq for merging?

[sam-github]

@tobespc @rwalle61 diff is uncovered because I moved original code (that was uncovered). Since the coverage is unrelated to this PR, can we merge this? Its blocking https://github.com/appsody/stacks/issues/447

[sam-github]

codebeat hates onIoConnection(), but its existing code, and I'm not sure how to make it happy.

@tobespc PTAL

[mattcolegate]

I'll have a look as Toby's not in today

[sam-github]

@mattcolegate look merge and publishable now? checks have passed.

[sam-github]

Thanks @tobespc