Improve zonemgr validator and normalizer
    
    The validator has been improved to support better both SOA format
    (e-mail address in a domain name format, without '@') and standard
    e-mail format. Allow '\.' character in a SOA format encoding the
    standard '.' in the local-part of an e-mail. Normalization code
    has been moved to one common function.
    
    https://fedorahosted.org/freeipa/ticket/2053