MB-8301: enable XDCR to replicate to remote memcached

Change-Id: I3a66870c16364fee584bb97fea84b856032ce254
Merge branch 'xmemtoy' of github.com:xiejunyi/ns_server into 202test

Conflicts:
	src/xdc_vbucket_rep_xmem_worker.erl

Change-Id: Iac0fa4bc5ccb174cd8e0ff970f70cd17bf2ae77a