Jaeger cleantempfiles

[aldas]

See: labstack/echo#2413

---

alright, to summarize this situation:

we are leaking temporary files because when jaegertracing replaces original Request object with new one with its span added to the context.Context.

echo-contrib/jaegertracing/jaegertracing.go

Line 200 in 5bb0f68

c.SetRequest(req)

			req = req.WithContext(opentracing.ContextWithSpan(req.Context(), sp))
			c.SetRequest(req)

problem with that is when c.FormValue or c.FormFile is used in handler (upload) that new Request object parses multipartform object. Creates new temporary file and sets form as it field.

now these temporary form files are cleaned up at the end of the request by go standard library HERE but http server does not have access to that new Request object - it still works on that old Request object that does not have parsed form, therefore does not know anything about temporary files.

---

problem must be fixed where it is introduced. - jaegertracing middleware must clean multipartform files at the end of its lifecycle.

[codecov]

Codecov Report

Patch coverage: 75.00% and project coverage change: +0.04 🎉

Comparison is base (5bb0f68) 58.79% compared to head (8ed8dca) 58.84%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #90      +/-   ##
==========================================
+ Coverage   58.79%   58.84%   +0.04%     
==========================================
  Files           8        8              
  Lines         682      690       +8     
==========================================
+ Hits          401      406       +5     
- Misses        258      260       +2     
- Partials       23       24       +1     

Impacted Files	Coverage Δ
jaegertracing/jaegertracing.go	56.37% <75.00%> (+0.25%)	⬆️

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