reliability models - minor usability enhancements
    display low probabilities in exponential format
    replace site repair time with availability
            (more intuitive, but people will surely get it wrong)
    add parameters for node FITs, async rep latency and fullness

Signed-off-by: markkampe <mark.kampe@inktank.com>
reliability model - add support for tunable volume fullness

Signed-off-by: markkampe <mark.kampe@inktank.com>
reliability model - minor corrections/extensions
	add multi-site reliability to default output
	scale remote recovery failure exposure to #involved drives
        remote recovery failure loses no more data than local failure did

Signed-off-by: markkampe <mark.kampe@inktank.com>