Make set_config.py compatible with both Py2 and Py3
Make set_config.py compatible with both Py2 and Py3

When asserting the validity of config files, we currently
use viewkeys(), which has been removed in Python3, so a kolla
container cannot set the config with Python3 only.

  "Traceback (most recent call last):",
  "  File \"/usr/local/bin/kolla_set_configs\", line 406, in main",
  "    config = load_config()",
  "  File \"/usr/local/bin/kolla_set_configs\", line 297, in load_config",
  "    validate_config(config)",
  "  File \"/usr/local/bin/kolla_set_configs\", line 238, in validate_config",
  "    if not data.viewkeys() >= required_keys:",
  "AttributeError: 'dict' object has no attribute 'viewkeys'"

Use keys() instead, which is compatible with both Python2 and
Python3, and has no visible performance disadvantage and wrap it in a
set() call so that we are guranteed to compare sets.

Change-Id: I5f53c8f5a390a9df3ebb60659ebdcef41e3a9cad
Co-Authored-By: Michele Baldessari <47483730395cccb6448ad7313d5cedb48de25e40@acksyn.org>

rahulunair/kolla,stackforge/kolla,openstack/kolla,stackforge/kolla,rahulunair/kolla,stackforge/kolla,openstack/kolla