'Set I{nonce} which is arbitraty set of bytes to prevent
reply attacks.
@param text: The nonce text value.
Generated when I{None}.
@type text: str'

def setnonce(self, text=None):

    if (text is None):
        s = []
        s.append(self.username)
        s.append(self.password)
        s.append(Token.sysdate())
        m = md5()
        m.update(':'.join(s))
        self.nonce = m.hexdigest()
    else:
        self.nonce = text
