dbus: skip FB303 in demo code if import failed
dbus: skip FB303 in demo code if import failed

FB303 depends on Thrift. The demo code exits with ImportError if Thrift
is not available.

fmoo/sparts,djipko/sparts,facebook/sparts,fmoo/sparts,djipko/sparts,bboozzoo/sparts,facebook/sparts,bboozzoo/sparts