allow undefined request in audit api
allow undefined request in audit api

to support reset_password and potentially node shutdown which are not
initiated by http request

Change-Id: I2abab1aebc29af33b20bd7e9eb388ad89e0d8699
Reviewed-on: http://review.couchbase.org/43219
Reviewed-by: Aliaksey Kandratsenka <340b8e09ca65cd3fc686427fcfed17e87eaf61e2@gmail.com>
Tested-by: Aliaksey Kandratsenka <340b8e09ca65cd3fc686427fcfed17e87eaf61e2@gmail.com>

membase/ns_server,membase/ns_server,mschoch/ns_server,nimishzynga/ns_server,nimishzynga/ns_server,ceejatec/ns_server,mschoch/ns_server,ceejatec/ns_server,mschoch/ns_server,membase/ns_server,nimishzynga/ns_server,ceejatec/ns_server,membase/ns_server,nimishzynga/ns_server,mschoch/ns_server,membase/ns_server,mschoch/ns_server,ceejatec/ns_server,membase/ns_server,ceejatec/ns_server,ceejatec/ns_server,nimishzynga/ns_server,nimishzynga/ns_server,mschoch/ns_server