Harden ZMQ in case of "EINTR" exception

[tomuben]

Background

ZMQ might raise a "EINTR" exception if a signal occured during processing of blocking calls (send, recv, etc.).
Check for example: http://api.zeromq.org/4-2:zmq-recv =>

EINTR
The operation was interrupted by delivery of a signal before a message was available.

Please note, it affects all kinds of ZQM calls (recv, send, setsockopt, connect, ...)

In this case we need to retry the respective operation.

Acceptance

Implement a retry mechanism for all ZMQ calls.