Add "line of death" to node storage info.
Add "line of death" to node storage info.

This is the minimum amount of free space on a node multiplied by the
number of nodes. It is intended to provide an estimate of the amount
of usable space remaining.

Change-Id: I7a67759ccb977b6b2b7fdbc5a9b214e8c5000b06
Reviewed-on: http://review.membase.org/4109
Tested-by: Aliaksey Kandratsenka <340b8e09ca65cd3fc686427fcfed17e87eaf61e2@gmail.com>
Reviewed-by: Aliaksey Kandratsenka <340b8e09ca65cd3fc686427fcfed17e87eaf61e2@gmail.com>

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