wsgi: make sure eventlet process is stopped before httpd

wsgi: make sure eventlet process is stopped before httpd

When stopping Ceilometer API running eventlet (ceilometer-api service),
we need to make sure it's done *before* starting Apache.

Otherwise, there is a race condition where Apache could be started before
stopping the service, and what would lead to:

AH00072: make_sock: could not bind to address [::]:8777
AH00072: make_sock: could not bind to address 0.0.0.0:8777
no listening sockets available, shutting down

Apache fails to start.

This patch make sure we have the right orchestration in place.

Change-Id: Ieec365b9eed2a13d132005118f93089ac9885e58