ipautil: new functions kinit_keytab and kinit_password
    
    kinit_keytab replaces kinit_hostprincipal and performs Kerberos auth using
    keytab file. Function is also able to repeat authentication multiple times
    before giving up and raising Krb5Error.
    
    kinit_password wraps kinit auth using password and also supports FAST
    authentication using httpd armor ccache.
    
    Reviewed-By: Jan Cholasta <jcholast@redhat.com>
    Reviewed-By: Simo Sorce <ssorce@redhat.com>
    Reviewed-By: Petr Spacek <pspacek@redhat.com>