Extract separate class TurbineClustersProvider to be able to provide custom solution for retrieving configured clusters (#2219)

See https://github.com/spring-cloud/spring-cloud-commons/issues/265

see https://github.com/Netflix/archaius/pull/522

Port information was missing from data sent to eureka.

fixes gh-2372

The message has to be sent after the endpoint starts up, which only
happens after the first request is accepted, so we put that logic
in the response extractor.

* Allow init params to be set on ProxyStreamServlet.

Fixes gh-2301

* Added unit test for #gh-2301

Modfied RibbonCommandContext to make request entity resettable. fixes gh-892

* Remove @EnableDiscoveryClient and @EnableEurekaClient as there are now optional.  Fixes #2241.

SpringMvcContract: Ignore RequestMapping headers with no value.

According to:

https://docs.spring.io/spring/docs/current/javadoc-api/org/springframework/web/bind/annotation/RequestMapping.html#headers--

the `headers` field can take several formats:

1. Require the header with a concrete value: `"My-Header=myValue"`
2. Require the header with any value: `"My-Header"`
3. Require the header is absent: `"!My-Header"`
4. Require the header with a negated value : `"My-Header!=myValue"`

This fixes `parseHeaders` for cases 2-4 (which previously threw a `StringIndexOutOfBoundsException`).

Fixes gh-1778.

* simplify org.springframework.cloud.netflix.zuul.filters.ProxyRequestHelper#setResponse

* Update ProxyRequestHelper.java

Fallback cause is propagated to fallback provider

Adjust Ribbon connect and read timeout values

Cause can now be propagated to fallback provider in order to respond accordingly to a exception type.
New interface is introduced in order not to break any existing falback providers.

Update rxjava version