python3: Compatibility for iteritems differences

In python3 dict.iteritems(), dict.iterkeys(), and
dict.itervalues() are no longer supported. So use
six.iteritems() where it is appropriate.

Change-Id: I8b07dc2a89d790ec275d45f859e1644e9b00c837
Signed-off-by: Chuck Short <chuck.short@canonical.com>
Merge "python3: Compatibility for iteritems differences"