R1:0364ccdd5f4d

Fix an issue where PhabricatorWorkerLeaseQuery may lease different tasks than it selects

Summary:
We lock tasks by setting `leaseOwner` to a unique value, but the value is currently unique-to-the-process rather than unique-to-the-query. This means that if a process leases a task, then leases another task, both tasks will have the same `leaseOwner`. This can cause an issue where we go to select the task we just leased and get the other task instead, if we aren't careful about the select construction.

We…