Use input method from python six

Something our unittests didnt catch which is more functional
than anything. Using raw_input fails on python3 because it was
renamed to input. Six provides an alias that handles both
cases.

Signed-off-by: Adam Stokes <adam.stokes@ubuntu.com>
Merge branch 'master' of github.com:sosreport/sos into bmr-fedora-py3