Use VirusTotal with python3 (issue #361)

[Nergie]

Force VirusTotal analyzers to use python3 (issue #361)

• Fix error ImportError: No module named 'StringIO'
  Old:

 import os
import StringIO
try:
    import requests
except ImportError:
pass

New:

import os
try:
    import requests
    import StringIO
except ImportError:
    from io import StringIO
    pass

• Fix "fatal error"
  Old: print >> sys.stderr, str(results.get('verbose_msg'))
  New: print (str(results.get('verbose_msg')), sys.stderr)