fixed logger crash while logging start of engage_cluster
fixed logger crash while logging start of engage_cluster

Change-Id: Ia8faec29b5a5623aefd07a2bb23557ae7f16a181
Reviewed-on: http://review.couchbase.org/11230
Tested-by: Aliaksey Artamonau <3c875bcfb3adf2a65b2ae7686ca921e6c9433147@gmail.com>
Reviewed-by: Aliaksey Artamonau <3c875bcfb3adf2a65b2ae7686ca921e6c9433147@gmail.com>

nimishzynga/ns_server,ceejatec/ns_server,vzasade/ns_server,ceejatec/ns_server,membase/ns_server,t3rm1n4l/ns_server,daverigby/ns_server,membase/ns_server,mschoch/ns_server,membase/ns_server,nimishzynga/ns_server,t3rm1n4l/ns_server,mschoch/ns_server,daverigby/ns_server,daverigby/ns_server,pavel-blagodov/ns_server,mschoch/ns_server,vzasade/ns_server,ceejatec/ns_server,nimishzynga/ns_server,t3rm1n4l/ns_server,nimishzynga/ns_server,vzasade/ns_server,mschoch/ns_server,pavel-blagodov/ns_server,pavel-blagodov/ns_server,membase/ns_server,nimishzynga/ns_server,mschoch/ns_server,t3rm1n4l/ns_server,t3rm1n4l/ns_server,daverigby/ns_server,vzasade/ns_server,membase/ns_server,nimishzynga/ns_server,ceejatec/ns_server,ceejatec/ns_server,mschoch/ns_server,pavel-blagodov/ns_server,daverigby/ns_server,ceejatec/ns_server,membase/ns_server