Update an existing SLA.
sla.update <slaName=name|slaSerial=serial>
[,newName=<string>]
[,comment=<string>]
[,threshold=<percent>]
[,minGranularity=<week|day|hour|minute>]
[,scheduleName=<value>]
Note that you cannot change the calculationPeriod
of an existing SLA test.