Make Hystrix Thread Pool available while using Zuul 

Upgrade Feign to 9.3.0

Upgrade Feign to 9.2.0

fixes gh-1266

Conflicts:
	spring-cloud-netflix-core/src/test/java/org/springframework/cloud/netflix/ribbon/RibbonClientConfigurationTests.java

fix 'RibbonRequest' cannot to encode issues

Merge branch 'master' of https://github.com/spring-cloud/spring-cloud-netflix into zuul_hystrix_threadpool

This reverts commit 21df6e43.

A problem in Spring Boot means that the extra conditions are combined
with OR not AND, so it's a bug to have more than one until that
gets fixed (in an AnyNestedCondition).

See https://github.com/spring-projects/spring-boot/pull/6672

Merge branch 'context-path-prefix-support' of https://github.com/kakawait/spring-cloud-netflix into kakawait-context-path-prefix-support

- add zuul.add-host-header property to add Host header
- add port to X-Forwarded-Host as defined in RFC 7239
- extract PreDecorationFilter.filterOrder() into a public constant

fixes gh-1108

Add a check to current context as contentLength is already in the context
Get content length from Headers when RibbonCommandContext is built + add tests
Use request content length RibbonRoutingFilter
Add documentation for new zuul.ribbonIsolationStrategy property

fixes gh-339

What we're missing ATM is different documentation versions for different application versions. What this change does is that it's:

- finding out what is the current branch (e.g. 1.0.x)
- finding out out what is the name of the main adoc file (e.g. spring-cloud-sleuth)
- pulling the changes from gh-pages after checkout
- finding out what is the list of comma separated whitelisted branches (via the `docs.whitelisted.branches` prop)
- in gh-pages creating a folder with name of the branch  (e.g. /1.0.x)
copying all the docs/target/generated-docs/ to that folder
- if the branch from which we're calling the script is NOT master then we're changing the ${main.adoc}.html to index.html so that it's easier to access the docs (e.g. http://cloud.spring.io/spring-cloud-sleuth/1.0.x/)

Expose security context to any Hystrix command.

* pull1242:
  Add @Qualifier customization for @FeignClient

Changed test to use @Qualifier.
Add documentation to reference the new attribute.

fixes gh-1240