Allow --data option to pass UUID instead of json

Allow the user to pass UUID only instead of full json.  This will
be handy for get and delete.  For example:

    python -m examples.get openstack/network/v2/network.py \
           --data ab13c9e7-3f30-4eee-9f96-41deb0223183

Change-Id: I12f15728b908d21110e9dead857d24d903bf17a9
Merge "Allow --data option to pass UUID instead of json"