PROTON-2091: fix `len(queue)` in python/examples and reformat for PEP8
PROTON-2091: fix `len(queue)` in python/examples and reformat for PEP8

astitcher/qpid-proton,ssorj/qpid-proton,apache/qpid-proton,apache/qpid-proton,ssorj/qpid-proton,ssorj/qpid-proton,ChugR/qpid-proton,apache/qpid-proton,apache/qpid-proton,ssorj/qpid-proton,gemmellr/qpid-proton,astitcher/qpid-proton,ssorj/qpid-proton,ChugR/qpid-proton,gemmellr/qpid-proton,ChugR/qpid-proton,apache/qpid-proton,gemmellr/qpid-proton,gemmellr/qpid-proton,astitcher/qpid-proton,kgiusti/qpid-proton,ChugR/qpid-proton,astitcher/qpid-proton,ssorj/qpid-proton,kgiusti/qpid-proton,gemmellr/qpid-proton,kgiusti/qpid-proton,ChugR/qpid-proton,gemmellr/qpid-proton,kgiusti/qpid-proton,kgiusti/qpid-proton,kgiusti/qpid-proton,ChugR/qpid-proton,astitcher/qpid-proton,apache/qpid-proton,astitcher/qpid-proton