Fix error for SigV4 version s3

[jiajie999]

Get error When delete files in s3 mumbai region.
Solved it by adding "host" parameter and use "OrdinaryCallingFormat"

[2017-11-29@10:05:34] INFO: Getting subdirs to feed to list threads
[2017-11-29@10:05:34] ERROR: Uncaught exception
Traceback (most recent call last):
  File "./s3wipe", line 241, in <module>
    main()
  File "./s3wipe", line 186, in main
    aws_secret_access_key=args.key)
  File "/usr/local/lib/python2.7/site-packages/boto/s3/connection.py", line 197, in __init__
    "When using SigV4, you must specify a 'host' parameter."
HostRequiredError: BotoClientError: When using SigV4, you must specify a 'host' parameter.