Ease zonemgr restrictions
    
    Admin e-mail validator currently requires an email to be in
    a second-level domain (hostmaster@example.com). This is too
    restrictive. Top level domain e-mails (hostmaster@testrelm)
    should also be allowed.
    
    This patch also fixes default zonemgr value in help texts and man
    pages.
    
    https://fedorahosted.org/freeipa/ticket/2272