test_address_get_if_addrs_[ifaddrs,win32]() will assert instead of failing gracefully.

Reported here: https://lists.torproject.org/pipermail/tor-talk/2015-April/037541.html

Passing in severity of 0, instead of LOG_ERR causes the logging code to assert. Mostly harmless since the test was going to fail anyway, but should be fixed to fail in a more graceful manner.