Catch the X-Forwarded-For header

As in apache2 virtual host config for keystone_wsgi uses
CustomFormat, which applies possible X-Forwarded-For header,
we should try to match it, to avoid `pattern not match` in Fluentd.

Change-Id: I10009b949568990a5fc6a76a33f53bc26214ea20
Closes-Bug: PROD-21786
1 file changed