MB-15171: [BP] Initialize dcpConnMap_ to NULL in engine constructor
MB-15171: [BP] Initialize dcpConnMap_ to NULL in engine constructor

Not initializing this variable to NULL can cause access to an
invalid pointer during engine destroy.

Change-Id: Icc5d848f7826bb6331deb40b4832efcf64622dea
Reviewed-on: http://review.couchbase.org/51492
Reviewed-by: Chiyoung Seo <fcffc23db27b19ee4ebba46695ee6b50e09216a2@couchbase.com>
Reviewed-by: abhinav dangeti <d73ef2279de6577f7bf081737ee47554bbb7dc82@couchbase.com>
Tested-by: buildbot <80754af91bfb6d1073585b046fe0a474ce868509@couchbase.com>
Reviewed-on: http://review.couchbase.org/56171

daverigby/ep-engine,owendCB/ep-engine,owendCB/ep-engine,hisundar/ep-engine,daverigby/kv_engine,daverigby/kv_engine,daverigby/kv_engine,hisundar/ep-engine,couchbase/ep-engine,hisundar/ep-engine,teligent-ru/ep-engine,membase/ep-engine,daverigby/ep-engine,daverigby/ep-engine,couchbase/ep-engine,teligent-ru/ep-engine,couchbase/ep-engine,teligent-ru/ep-engine,couchbase/ep-engine,daverigby/ep-engine,membase/ep-engine,daverigby/kv_engine,teligent-ru/ep-engine,hisundar/ep-engine,membase/ep-engine,owendCB/ep-engine,owendCB/ep-engine,membase/ep-engine