Add a test for a NO or BAD response for FETCH and STORE

With #94 we are checking for EOF and similar kind of errors, but there is no check that response is actually OK as long as we get any tagged response. In case of STORE a NO response means we actually failed to store anything, and in case of FETCH it means that no responses not necessarily indicate there no messages, just that IMAP server lost connection to its NFS server or there is a loose SATA cable resulting in a disk read failure.