'read_until(expected, timeout=None)
test the blocking version of read_util'

def test_read_until(self):

    want = ['xxxmatchyyy']
    telnet = test_telnet(want)
    data = telnet.read_until('match')
    self.assertEqual(data, 'xxxmatch', msg=(telnet.cookedq, telnet.rawq, telnet.sock.reads))
    reads = [('x' * 50), 'match', ('y' * 50)]
    expect = ''.join(reads[:(-1)])
    telnet = test_telnet(reads)
    data = telnet.read_until('match')
    self.assertEqual(data, expect)
