This change reduces retries during cluster health validation. There are
multiple retry levels today:
* retry on urllib3 http level
* retry in validating cluster health
* retry in _proxy_internal
This causes retry storm, which brings significant delays to API calls.
This is especially relevant when nsxlib is configured with
cluster_unavailable_retry = True (this is always the case with single
endpoint).
This change reduces configurable retry attempts in cluster health
validation to single retry per endpoint.
In addition, this change fixes scenario when client configures nsxlib
with no validation, in which case cluster should not mark endpoint as
UP in validation related code.
Change-Id: I33b4101a0e0c0f4088e10776e126cc495dabd89c
1e675ae459