Add XML support to tests that currently have only JSON calls

Add XML support to Compute tests that currently have only JSON calls. I have identified the following scripts that do not have XML support:
1)Compute:
     a) quotas_client: DONE
     b)console_output_client: DONE
2) images tests:
     a) test_image_metadata.py: DONE
     b) test_images_whitebox.py:- NOT to be done
     c) test_list_image_filters.py: DONE
     d) test_list_images.py: DONE
3) servers tests:
     a) test_console_output.py: DONE (Rajalakshmi Ganesan)
     b) test_disk_config.py; - DONE (Ivan Zhu)
     c) test_list_servers_negative.py: DONE (Rajalakshmi Ganesan)
     d) test_server_addresses.py: DONE(Matthew Treinish)
     g) test_server_metadata.py: DONE(Meera Belur)
     h) test_servers_negative.py: DONE
     j) test_servers_whitebox.py: NOT to be done - The Test script is being skipped even for JSON, Also base class is not using _interface variable. Need to find alternative way to add XML support.
4) scripts in /tests/compute/
     a) test_authorization.py: DONE
     b) test_live_block_migration.py: DONE

5) Tests that use nova_client

     a) test_server_advanced_ops.py;
     b) test_server_basic_ops.py

DONE: Merged into repo