Change Credentials header to Blob from data
Change Credentials header to Blob from data

The payload data of credentials is the unfortunately named blob.
Currently when listing credentials the payload is excluded as OSC is
looking for a column called data which does not exist.

Change-Id: I6fa4579d7ec9ba393ede550191dbd8aa29767bf4

redhat-openstack/python-openstackclient,BjoernT/python-openstackclient,redhat-openstack/python-openstackclient,dtroyer/python-openstackclient,openstack/python-openstackclient,openstack/python-openstackclient,dtroyer/python-openstackclient,BjoernT/python-openstackclient