weighted lease

[a8m]

for example:

leaseKey	leaseOwner	leaseWeight	leaseCounter
task 1	worker 1	1 (default)	x
task 2	worker 2	3	x
task 3	worker 1	1 (default)	x
task 4	worker 1	1 (default)	x

comments:

• the default weight of a lease(or task) is 1
• we expect the leaser to partition the work according to the total weight of the tasks.