Ensure that keystone uses global debug setting

When setting ENABLE_DEBUG_LOG_LEVEL the keystone screen would ignore
this setting and always use the debug mode.

Change-Id: I934443c2976e936198fc93da4cca717e6cb84e6f
Allow ceilometer-api to run under mod_wsgi

If CEILOMETER_USE_MOD_WSGI is True then the API app will
run under mod wsgi. The default is false (for now).

The changes are modeled on keystone's use of apache.

Note that these changes are dependent on
https://review.openstack.org/#/c/121823/ in ceilometer.

Using mod_wsgi allows the ceilometer api to handle "concurrent"
requests. This is extremely useful when trying to benchmark
various aspects of the service.

Change-Id: I4c220c3b52804cd8d9123b47780a98e0346ca81e
Merge "Ensure that keystone uses global debug setting"
Merge "Allow ceilometer-api to run under mod_wsgi"
Merge branch 'master' of https://github.com/openstack-dev/devstack