Unlike uwsgi, apache mod_wsgi does not support passing
commandline arguments to the python wsgi script it invokes.
As a result while you can pass --config-file when hosting the
api and metadata wsgi applications with uwsgi there is no
way to use multiple config files with mod_wsgi.
This change mirrors how this is supported in keystone today
by intoducing a new OS_NOVA_CONFIG_FILES env var to allow
operators to optional pass a ';' delimited list of config
files to load.
This change also add docs for this env var and the existing
undocumented OS_NOVA_CONFIG_DIR.
Closes-Bug: 1994056
Change-Id: I8e3ccd75cbb7f2e132b403cb38022787c2c0a37b
73fe84fa0e