existing strategy if present. Fixes #2035

Previously, these were managed directly via archaius, but due to
some combination of changes in boot 1.5.x (likely a tomcat change as
zuul filters were initialzed in a servlet context listener) and Dalston,
The filter was created before archaius could be initialized.

The properties are backwards compatible and are in the
`ZuulProperties.Host` object.

fixes gh-1950

spring boot uses all high ports and there are some trouble if ports end with 443 (e.g. 24443, ...)

Let SecurityContextConcurrencyStrategy be installed as the hystrix
concurrency strategy regardless of if feign's hystrix support is installed.

fixes gh-1969

The timeToLive and timeUnit parameters added to configure connection pool.

Fixes gh-1720

Fixes gh-1598

CounterFactory is used by ZuulException and was previously initialzed
with a dummy impl.

This adds a Spring Boot CounterService based implementation.

Also adds the ability to implement a zuul TracerFactory.

Add the ability for ribbon clients to specify response status codes they would like to retry.  Fixes #1540.

fixes gh-1824

Change /routes endpoint to use EndpointMvcAdapter and AbstractEndpoint.  

Fixes #1797

Add X-Forwarded-Port header in Zuul PreDecorationFilter
even with X-Forwarded-Host header being absent.

By default, `LoadBalancerBuilder` built a load-balancer with a `PollingServerListUpdater`. This change introduces a `ServerListUpdater` bean which creates a `PollingServerListUpdater(IClientConfig)` so that `ribbon.ServerListRefreshInterval` is respected.

 fixes gh-1304