* Add support loadBalancerKey in RibbonRoutingFilter

* Add documentation about how to provide a loadBalancerKey to Ribbon

* Add integrationtest for RibbonRoutingFilter's loadBalancerKey support

* Adds backoff policies when retrying requests.  Fixes #2195

* fixing final variable

* Add new Zuul filters endpoint and refactor routes endpoint
* Refactor FiltersEndpoint
- Extend from AbstractEndpoint and simplify code
- Move tests classes into package endpoint
- Remove usage of Lombok
* Conditionally enable Zuul routes and filters endpoints
* Provide FilterRegistry to FiltersEndpoint via constructor

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

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

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

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

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.

* Introduce getRoutesMap() so subclasses can have read/write access to configured/discovered routes.

Signed-off-by: Gregor Zurowski <gregor@zurowski.org>

Otherwise useServlet31 was always returning false.

fixes gh-2196

Signed-off-by: João Salavessa <joao.salavessa@sky.uk>

(Updated okhttp3 from v3.6.0 to v3.8.1)

Fixes gh-665

fixes #1741