Avoid thundering herd when SoftwareProcess rebinds its sensors

Applies a random delay of up to 10s before an entity calls
connectSensors(). Without the delay all entities attempt to reconnect
at once, which regularly causes SSH connection refused errors if
several of the entities are running on the same machine. This doesn't
guarantee to avoid the problem but makes it much less likely.
Allows configuration of rebind-sensors delay

Set config key to null or to == Duration.ZERO to connect sensors
immediately.
Merge pull request #1318 from sjcorbett/ssh-connection-refactor

Avoid thundering herd when SoftwareProcess rebinds its sensors