Currently there's a boolean KEYSTONE_USE_MOD_WSGI to switch between
running keystone in mod_wsgi and eventlet. We've got a need to
support more/different deployment options (e.g., uwsgi), so a
boolean is inadequate.
A new input variable KEYSTONE_DEPLOY is introduced that can be
set to mod_wsgi or eventlet (and other values in future) to
control how keystone is deployed. KEYSTONE_USE_MOD_WSGI is
deprecated.
Change-Id: I9b2815e6f007309f088346df9ac48e6a24ae3656
a03053660a