Add support for Python 3

Add support for Python 3

Porting to Python3 using Openstack guidelines:
https://wiki.openstack.org/wiki/Python3

This passes unittests on Python 3.5 and passes opnfv_smoke suite

Updates:
   use six for urlparse and urlopen
   fix exception.message attribute removal
   run unittests on python3
   use unitest.mock on python 3
   fix open mock for vsperf
   fix float division by using delta/eplison comparison
   use unicode in StringIO
   use plugin/sample_config.yaml relative path from test case
   fixed apexlake unittests
   upgraded to mock 2.0.0 to match python3 unittest.mock features
   fixed flake8 issues
   implement safe JSON decode with oslo_serialization.jsonutils.dump_as_bytes()
   implement safe unicode encode/decode with oslo_utils.encodeutils

heat: convert pub key file from bytes to unicode
    pkg_resources returns raw bytes, in python3
    we have to decode this to utf-8 unicode
    so JSON can encode it for heat template

JIRA: YARDSTICK-452

Change-Id: Ib80dd1d0c0eb0592acd832b82f6a7f8f7c20bfda
Signed-off-by: Ross Brattain <ross.b.brattain@intel.com>