fix: avoid requests to invalid hostname

Implementation of net_box in tarantool-module resolves hostnames with a to_socket_addrs function that is blocking. Pytest uses fake addresses in one test, and sometimes it results in 5-second blockage and consequent test failure.

This patch only provides a workaround. It makes a connection to fail even before the blocking DNS request.

See also:

• tarantool-module#81 (closed)