locking.LockSet: Implement acquire timeouts

The timeout passed to LockSet.acquire() is measured over all lock acquires. If
LockSet.acquire fails to acquire all requested locks within the specified
amount of time, all locks are released again and the acquire fails.

Signed-off-by: Michael Hanselmann <hansmi@google.com>
Reviewed-by: Guido Trotter <ultrotter@google.com>