bp:MB-100 use sockets pool for long blocking memcached calls

so far it is just wait_for_checkpoint_persistence but there
will be more of them

Change-Id: Iaeca8739de6358e2309d07c04d2a9a18dca63be6
Orig-Reviewed-on: http://review.couchbase.org/32748
Reviewed-on: http://review.couchbase.org/34029
Reviewed-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
bp:MB-100 allow free form Destination in ns_connection_pool

there's no need to require it to be {Host, Port, Ssl}

Change-Id: Icee603aeab20a5199a640abb2c2ce89dd00b6a8b
Orig-Reviewed-on: http://review.couchbase.org/32747
Reviewed-on: http://review.couchbase.org/34030
Reviewed-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
bp:MB-100 dialyzer fix

Change-Id: Id738748957f12da4accd5a03174dfb18d3531f53
Orig-Reviewed-on: http://review.couchbase.org/32828
Reviewed-on: http://review.couchbase.org/34031
Reviewed-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Merge commit '2ddb54cfbaaa7...' into merge

* commit '2ddb54cfbaaa7754d00b84be32f3ad1fd6c1a589':
  bp:MB-100 dialyzer fix
  bp:MB-100 allow free form Destination in ns_connection_pool
  bp:MB-100 use sockets pool for long blocking memcached calls

Conflicts:
	src/ns_memcached.erl

This is merge of backports and therefore diff is empty

Change-Id: I7fe7771a3d3ad504f722e30f1c722c3992652825
Merge "Merge commit '2ddb54cfbaaa7...' into merge"