fix DBusRemote using the wrong attribute

[lilydjwg]

fixes this:

>>>bus=pystemd.dbuslib.DBusRemote(b'myhost')
>>>bus.open()
Traceback (mostrecentcalllast):
File"<stdin>", line1, in<module>File"pystemd/dbuslib.pyx", line303, inpystemd.dbuslib.DBus.openrets=self.open_dbus_bus()
File"pystemd/dbuslib.pyx", line577, inpystemd.dbuslib.DBusRemote.open_dbus_busreturndbusc.sd_bus_open_system_remote(&(self.bus), self.remote)
AttributeError: 'pystemd.dbuslib.DBusRemote'objecthasnoattribute'remote'

[lilydjwg]

Also fix use-after-free which shows up at the python interactive shell.

The CI failures are some fedora distributions failing to find and install cython.