Move common code so RibbonRoutingFilter can use the same code.

Fixes gh-407

Fixes gh-377

This reverts commit 0d468b39.

ref gh-383

fixes gh-374

See gh-377

fixes gh-372

Should be no change for users of Boot 1.2 right now, but with this
patch it is possible to use 1.3 with the new conventions for metrics
(e.g. in particular exporting by declaring beans of type
MetricWriter)

fixes gh-347

fixes gh-348

 fixes gh-350

fixes gh-324

fixes gh-323

https://github.com/spring-cloud/spring-cloud-netflix/issues/312)

fixes gh-307

When the Apache HTTP client is being set up for the Ribbon client we can jump
in and explicitly set a cookie policy. Obviously, since the client will generally
be shared across sessions, the only sensible default is IGNORE_COOKIES.

I couldn't find a way round this without using deprecated APIs (but there
are other instances of that in our code because of the way Netflix uses
it, so maybe that doesn't matter).

Fixes gh-301

If the app has a context path then the route locator does not match
the whole requestURI (as provided by the raw servlet API), but Spring
has a utility for stripping it off, so we can just use that.

Fixes gh-270

If there is a default route (/**) then the ZuulHandlerMapping will
mask the /error path in a normal Spring Boot application. This change
makes it a special case so that ZuulHandlerMapping will never map
the /error route (the one specified by the ErrorController).

Fixes gh-284

fixes gh-280

fixes spring-cloud-samples/tests/issues/2

Fixes gh-271, fixes gh-272

This was kind of ugly, and caused a static usage of the eureka
DiscoveryCLient to become necessary again, just so the @Bean that is
provided for the user stays accurate (it has to be the one in the main
application context, even if the parent boot strap has different
instance metadata).

I tested with a vanilla Eureka server and config server, and used the
client in tests/eureka-first.

Fixes gh-268