Use six.viewkeys instead of dict.keys to avoid py2 to py3 problems
Use six.viewkeys instead of dict.keys to avoid py2 to py3 problems

This change fixes an 'RuntimeError: dictionary changed size during
iteration' error that is raised because of different behaviour between
python2 and python3. We use the six library to ensure that the behavior
is compatible across versions.

Change-Id: I0723ae10825e1e2d86789627895e3286d8c97602
Resolves-Bug: #1829304

mahak/neutron,openstack/neutron,mahak/neutron,openstack/neutron,openstack/neutron,mahak/neutron