Fix pipe client initialization exception (raised by parent initializer)

[jiri-lunacek]

PipeConnection used parent initializer, which resulted in accessing recv property of None on line 223

class Connection(object):

    def __init__(self, conn=None):
        self._conn = conn
        self.recv = self._conn.recv

This fix introduces noop initializer for PipeConnection object and initializes the parent when the socket is available.