Conditionally add headers.

[dev-priporov]

ignored headers are added in method buildZuulRequestHeaders in class ProxyRequestHelper in code below:

for (String header : zuulRequestHeaders.keySet()) {
	headers.set(header, zuulRequestHeaders.get(header));
}

I've added a condition to skip these headers:

for (String header : zuulRequestHeaders.keySet()) {
	if (isIncludedHeader(header)){
		headers.set(header, zuulRequestHeaders.get(header));
	}
}

Fixes gh-3036

[pivotal-issuemaster]

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[codecov-io]

Codecov Report

Merging #3047 into master will increase coverage by 0.43%.
The diff coverage is 50%.

@@             Coverage Diff              @@
##             master    #3047      +/-   ##
============================================
+ Coverage     65.88%   66.32%   +0.43%     
- Complexity     1439     1440       +1     
============================================
  Files           182      182              
  Lines          6750     6755       +5     
  Branches        813      814       +1     
============================================
+ Hits           4447     4480      +33     
+ Misses         1994     1966      -28     
  Partials        309      309

Impacted Files	Coverage Δ	Complexity Δ
...cloud/netflix/zuul/filters/ProxyRequestHelper.java	90.69% <50%> (-0.71%)	54 <0> (ø)
...amework/cloud/netflix/zuul/web/ZuulController.java	87.5% <0%> (-12.5%)	2% <0%> (ø)
...netflix/ribbon/ZonePreferenceServerListFilter.java	61.53% <0%> (-11.54%)	9% <0%> (-1%)
...oud/netflix/ribbon/okhttp/OkHttpRibbonRequest.java	78.72% <0%> (-1.72%)	8% <0%> (ø)
...strix/dashboard/HystrixDashboardConfiguration.java	25.24% <0%> (-0.25%)	5% <0%> (ø)
.../netflix/zuul/filters/post/SendResponseFilter.java	80% <0%> (+0.14%)	35% <0%> (ø)	⬇️
...etflix/turbine/stream/HystrixStreamAggregator.java	78.94% <0%> (+5.26%)	9% <0%> (+1%)	⬆️
...cloud/netflix/eureka/EurekaInstanceConfigBean.java	69.03% <0%> (+16.75%)	54% <0%> (+1%)	⬆️

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[dev-priporov]

are all success checks necessary to complete PR?

[ztgoto]

client -> zuul proxy -> api service.

After this change, how can zuul proxy not allow forwarding client header information to the api service but allow zuul to generate the same header information to the api service, because the client is not trusted, but the zuul proxy is trusted

[ryanjbaxter]

Please open a separate issue with a sample that demonstrates the problem