Client should be updated to follow /v2/events redirection responses

[timcharper]

In d2iq-archive/marathon#6211, we will change the behavior in 1.7.x to respond with a redirect call when /v2/events is requested from a standby/non-leader Marathon instance.

The code should be updated to follow redirects in such a case.

The old proxying behavior can be optionally extended until Marathon 1.8.x, at which point the old proxying will be totally removed.

See the changelog item for more details: https://github.com/mesosphere/marathon/pull/6211/files#diff-42ba1d994f4fa8c6ad17a7efae7936cc