ignore 4xx retry
optimize code
fixed callback failed code
add 6xx, 7xx code
Merge branch 'develop' of github.com:qiniu/python-sdk into retry-host
remove a mistake test
Merge pull request #121 from longbai/retry-host

忽略4xx的重试
#9891
Merge pull request #122 from coaku/b_xzk_upload_qiniu_com

#9891
Merge pull request #123 from qiniu/develop

Release 6.1.7