main.py: add missing six imports
main.py: add missing six imports

Caught by flake8:

    rhcephpkg/main.py:96:21: F821 undefined name 'HTTPError'
    rhcephpkg/main.py:96:32: F821 undefined name 'BadStatusLine'

red-hat-storage/rhcephpkg,red-hat-storage/rhcephpkg