Client retries if connection is not healthy(meaning its heartbeat is tim...

...ed out). ClientCallFuture does not return null when timeout, rethrows the exception.

fixes #2593 
from sona
https://hazelcast-l337.sonar.cloudbees.com/drilldown/measures/1?metric=coverage&rids%5B%5D=3#
we can see that this line has never been executed in a test