Provide new functions for memory quota validation/update.
Provide new functions for memory quota validation/update.

New functions to not assume homogeneity of cluster nodes.

Change-Id: I7a56e05b3de021092660f8894d54c3d0b23261c2
Reviewed-on: http://review.couchbase.org/54046
Reviewed-by: Aliaksey Artamonau <3c875bcfb3adf2a65b2ae7686ca921e6c9433147@gmail.com>
Tested-by: Aliaksey Artamonau <3c875bcfb3adf2a65b2ae7686ca921e6c9433147@gmail.com>

membase/ns_server,ceejatec/ns_server,ceejatec/ns_server,membase/ns_server,membase/ns_server,ceejatec/ns_server,ceejatec/ns_server,ceejatec/ns_server,membase/ns_server,membase/ns_server,ceejatec/ns_server,membase/ns_server