libtracker-miner: Check there's no other active operations

This function is called from monitor operations, and relies that there's
no previous operations being handled. This might well not be true, so
ensure the queues are idle before going ahead.
20 jobs for wip/carlosg/timeouts-and-stuff in 1 minute and 39 seconds
Status Job ID Name Coverage
  Test
passed #793726
test-fedora-latest

00:01:22

passed #793727
test-ubuntu-rolling

00:01:38

passed #793570
test-fedora-latest

00:01:32

passed #793724
test-fedora-latest

00:01:45

passed #793692
test-fedora-latest

00:01:21

passed #793644
test-fedora-latest

00:01:45

passed #793631
test-fedora-latest

00:01:25

passed #793612
test-fedora-latest

00:02:04

passed #793600
test-fedora-latest

00:01:26

passed #793576
test-fedora-latest

00:01:29

passed #793574
test-fedora-latest

00:02:32

passed #793575
test-ubuntu-rolling

00:01:20

passed #793599
test-ubuntu-rolling

00:02:18

passed #793693
test-ubuntu-rolling

00:01:54

passed #793725
test-ubuntu-rolling

00:01:19

passed #793645
test-ubuntu-rolling

00:02:15

passed #793571
test-ubuntu-rolling

00:01:31

passed #793632
test-ubuntu-rolling

00:01:35

failed #793577
test-ubuntu-rolling

00:01:27

passed #793613
test-ubuntu-rolling

00:01:18