Fixes gh-710

Apparently we already support eureka.datacenter as an alias for
archaius.deployment.datacenter and it looks like when that code
was written we intended to support eureka.environment in a similar way.
But it was never finished off, so this change adds the necessary one
line of code.

Fixes gh-791

Fixes gh-790

Since DiscoverClient now supports metadata natively, we can use that and not rely
on Eureka interafces at all.

Fixes gh-787. Also fixes https://github.com/spring-cloud/spring-cloud-config/issues/302

Eureka supports native placeholders, but Spring can also be used.
Added some docs to show how more explicitly.

See gh-761

fixes gh-573

fixes gh-781

fixes gh-779

fixes gh-777

Otherwise apps register the wrong health and status URLs by default. If
there is no explicit management.port we just need a default that is
the same as server.port.

A new integration test ill be added in spring-cloud-samples/tests.

Fixes gh-759

A change in Zuul in NetflixOSS means that it buffers all requests unless
you switch it off at the level of the servlet. And even when you do that
you need to ensure that Spring Cloud doesn't re-introduce a buffer through
the Servlet30RequestWrapper.

This change restores the feature in Spring Cloud Angel that multipart files
posted to /zuul/* go straight through the servlet and are not buffered in
memory.

Fixes gh-773

fixes gh-766

More often than not what Route.path was used it had to be concatenated
with the prefix. This change just encapsulates that concern in the
Route itself.

If it returns Routes instead of Strings it's a lot more obvious
what it's supposed.

Added @FeignClient(fallback).

Renamed FeignClientFactory to FeignContext.

fixes gh-762

fixes gh-727

The RouteLocator interface wasn't very useful to anyone in its
1.0.x form. If ProxyRouteLocator features are consolidated into
the RouteLocator interface then users can supply their own
strategies more easily.

Also added RefreshableRouteLocator for implementations that need
to recompute routes when something changes. SimpleRouteLocator
doesn't need to do that because all the routes are in the configuration.

Added spring-cloud-starter-archaius so downstream projects
like consul and zookeeper don't need to maintain the list of
archaius depenencies.

fixes gh-765

Servo and Spectator metrics defer to other Counter/GaugeServices

This move should be transparant to users of spring-cloud-starter-eureka.

fixes gh-579

The new module is a BOM that doesn't have any parent or direct
dependency management in spring-boot-*. So users can include it
in their dependency management without polluting the spring boot
dependency versions.

Luckily it can also be used in the main spring-cloud-netflix pom,
which should no longer be used as a BOM.