Asgard-2 - Retry Eureka calls on network failure

When a Eureka node has a problem while Asgard is trying to call it, Asgard should retry the call multiple times in an attempt to reach a working Eureka node. 

This should greatly reduce the chance of an Asgard user seeing an error due to Eureka having a hiccup.

It also should fix the problem of intermittently losing visibility into instance state during regular Chaos Gorilla drills and Eureka upgrades.