Add 6 cloud-init Azure specific cases and 1 general case

[zhaohuijuan]

1. test_cloudinit_auto_extend_root_partition_and_filesystem_azure - test_cloud_init.py, azure special
2. test_cloudinit_create_ovfenv_under_waagent_folder - test_cloud_init.py, azure special
3. test_cloudinit_enable_swap_in_temporary_disk - test_cloud_init.py, azure special
4. test_cloudinit_check_networkmanager_dispatcher - test_cloud_init.py, azure special
5. test_cloudinit_regenerate_sshd_keypairs - test_cloud_init.py, azure special
6. test_cloudinit_auto_register_with_subscription_manager_azure - test_cloud_init.py, azure special
7. test_cloudinit_publish_hostname_to_dns - test_cloud_init.py, general case which could run for all platforms