#335 Exception when creating non-exported tango devices

[Carlos Pascual]

In some situations (when tango device classes have been already registered), an attempt to create a TangoDevice for a non-existing device name results in an unhandled exception

This is the reason behind some of the test failures reported in [#334]

To reproduce:

import taurus
from taurus.core.tango.tangodevice import TangoDevice
class MyDev(TangoDevice):pass
f = taurus.Factory()
f.registerDeviceClass('foo', MyDev) # comment this out and the exception is gone
d = taurus.Device('a/b/nonexistent')

This will be fixed as part of the fixes of [#334]

[Zbigniew Reszela]

This bug was solved when integrating workaround for the ticket #334.