python3: Add python3 compatibility support

Add python2/python3 compatibility support:

- Use six.iteritems() to replace dictionary.iteritems()
  on python2 or dictionary.items() on python3.

- Use six.advanced_iterator as a replacement to call
  it.next() on python2 and next(it) on python3.

Change-Id: I48442696b66392de33520714b9beb2c645ec1b58
Signed-off-by: Chuck Short <chuck.short@canonical.com>
Add serializer param to RPC service

Allow a serializer to be passed to RPC service class
when it is instantiated.

Change-Id: I85dafc392023f0ae845efe851a5a4a9438e40e37
Merge "Add serializer param to RPC service"
Merge "python3: Add python3 compatibility support"