reliability model - cleanups of confusing parameters
	rename nre parameter to nre_model to elminate confusion w/rate
	change stripe width to stripe length because it is too esoteric

Signed-off-by: markkampe <mark.kampe@inktank.com>
reliability model - additional unit test cases
	site reliability and availability
	rados reliability effects of declustering factor

Signed-off-by: markkampe <mark.kampe@inktank.com>
reliability models - rename Pn/pn routines
	give Pn the more mnenmonic name of Pfail to highlight the diff

Signed-off-by: markkampe <mark.kampe@inktank.com>
reliability model - significant refactor/simplification of unit tests
	move most of the decision logic into a shared routine

Signed-off-by: markkampe <mark.kampe@inktank.com>
reliability models - cleanups
	RelyFuncts: prune imports, better encapsulate time units

Signed-off-by: markkampe <mark.kampe@inktank.com>
reliability model - first pass at multi-site unit test cases

Signed-off-by: markkampe <mark.kampe@inktank.com>
reliability models - first pass at a recursive descent multi-site model

Signed-off-by: markkampe <mark.kampe@inktank.com>
reliabiltiy model - document multisite, pass most of the tests
reliability model: dumb bug in async rep failure probability

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