Replace empty user with dash in access.log.
Replace empty user with dash in access.log.

Change-Id: I8d7863f27a31ea3a89ae7ef46db87d7a38bcde3d
Reviewed-on: http://review.couchbase.org/37940
Tested-by: Aliaksey Artamonau <3c875bcfb3adf2a65b2ae7686ca921e6c9433147@gmail.com>
Reviewed-by: Aliaksey Kandratsenka <340b8e09ca65cd3fc686427fcfed17e87eaf61e2@gmail.com>

nimishzynga/ns_server,mschoch/ns_server,membase/ns_server,mschoch/ns_server,t3rm1n4l/ns_server,membase/ns_server,ceejatec/ns_server,nimishzynga/ns_server,nimishzynga/ns_server,t3rm1n4l/ns_server,membase/ns_server,ceejatec/ns_server,ceejatec/ns_server,mschoch/ns_server,nimishzynga/ns_server,ceejatec/ns_server,mschoch/ns_server,mschoch/ns_server,t3rm1n4l/ns_server,membase/ns_server,membase/ns_server,mschoch/ns_server,membase/ns_server,nimishzynga/ns_server,nimishzynga/ns_server,ceejatec/ns_server,ceejatec/ns_server,t3rm1n4l/ns_server,t3rm1n4l/ns_server