fixes gh-822

fixes gh-406

fixes gh-813

fixes gh-809

Upgrading feign

Also does not rename another one because it fails (see gh-804). The
bug can be fixed in feign (https://github.com/Netflix/feign/pull/324),
and if that gets merged and released we can revert some of the recent
changes to the apache load balancer here.

fixes gh-807

See https://github.com/spring-cloud/spring-cloud-build/issues/26

Fix typo: zule-core -> zuul-core.

* spectator-issue-264:
  fix registration bug in SpectatorMetricServices

The primary change is to fix a memory leak reported in
Netflix/spectator#264. Each time a gauge was updated it
was creating a new registration and because the map holds
a strong reference these would never get collected.
Further, the aggregate value created by the multiple
registrations was not correct.

In addition I added some test cases around the various
inputs and checked that the results were reflected as
expected in the registry. I noticed the timer values
had a unit of milliseconds, but it isn't immediately
clear if the reported value can ever less than 1.0. The
conversion to long is now delayed until after converting
to nanoseconds so duration values less than 1.0 will now
work instead of just recording 0.

For the histogram I changed to just using a cast to `long`
to avoid boxing to a `Double`. As an FYI for the future,
there is a DoubleDistributionSummary we have experimented
with in spectator-ext-sandbox that might be more appropriate
for this use-case.

It is up to the user to configure a mapper if needed (one is no
longer provided automatically), so it doesn't need to take up
space in ZuulProperties

Fixes gh-803

So that it isn't instantated eagerly on startup by the RefreshScope.

Fixes gh-789

Tests are very sensitive to the Zuul RequestContext which is
thread bound.

The Apcahe client does not allow empty body for PATCH, nor does it
allow a request to be pre-populated with a Content-Length. Spring
Cloud tests were trying to do the former, and Feign allows the latter.

Change SimpleRouteLocator to work with both Zuul and DispatcherServlet

Fixes gh-794

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