Remote region registry lookup failure should not disable registry fetch

[NiteshKant]

Eureka server does not allow fetch registry if there is a remote region registry fetch configured and the remote region server is unavailable. Relevant code is here

This creates a circular dependency between two regions configured to fetch registry data from each other (which is typically the case) and hence makes it impossible to bootstrap two dependent regions.

This behavior should be altered such that remote region registry fetch is a 'best-effort' and any failure to retrieve this registry does not hamper clients fetching registry information.

Open question

Should we only disallow fetch registry calls that requires remote region data in this scenario?

[NiteshKant]

PR #158 fixes this issue.

Should we only disallow fetch registry calls that requires remote region data in this scenario?

This change disallows remote registry fetch calls when remote region registry is not available. The local region registry fetch is allowed.