Add WSGI support for `cloudkitty-api'

They dropped the cloudkitty-api command line[0], so we should add wsgi support for cloudkitty-api.

[0]https://review.openstack.org/#/c/366043/

docker logs cloudkitty_api:

INFO:__main__:Loading config file at /var/lib/kolla/config_files/config.json
INFO:__main__:Validating config file
INFO:__main__:Kolla config strategy set to: COPY_ALWAYS
INFO:__main__:Copying service configuration files
INFO:__main__:Deleting /etc/cloudkitty/cloudkitty.conf
INFO:__main__:Copying /var/lib/kolla/config_files/cloudkitty.conf to /etc/cloudkitty/cloudkitty.conf
INFO:__main__:Setting permission for /etc/cloudkitty/cloudkitty.conf
INFO:__main__:Writing out command to execute
INFO:__main__:Setting permission for /var/log/kolla/cloudkitty
INFO:__main__:Setting permission for /var/log/kolla/cloudkitty/cloudkitty-storage-init.log
INFO:__main__:Setting permission for /var/log/kolla/cloudkitty/cloudkitty-processor.log
INFO:__main__:Setting permission for /var/log/kolla/cloudkitty/cloudkitty-dbsync.log
Running command: 'cloudkitty-api --config-file /etc/cloudkitty/cloudkitty.conf'
usage: cloudkitty-api [-h] [--port PORT] [--host IP] -- [passed options]
cloudkitty-api: error: unrecognized arguments: --config-file