iotests: Make 030 less flaky

This patch fixes two race conditions in 030:

1. The first is in TestENOSPC.test_enospc().  After resuming the job,
   querying it to confirm it is no longer paused may fail because in the
   meantime it might have completed already.  The same was fixed in
   TestEIO.test_ignore() already (in commit
   2c3b44da07).

2. The second is in TestSetSpeed.test_set_speed_invalid(): Here, a
   stream job is started on a drive without any break points, with a
   block-job-set-speed invoked subsequently.  However, without any break
   points, the job might have completed in the meantime (on tmpfs at
   least); or it might complete before cancel_and_wait() which expects
   the job to still exist.  This can be fixed like everywhere else by
   pausing the drive (installing break points) before starting the job
   and letting cancel_and_wait() resume it.

Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-id: 20171109203025.27493-2-mreitz@redhat.com
Signed-off-by: Max Reitz <mreitz@redhat.com>

tests/qemu-iotests/030

@@ -666,6 +666,7 @@ class TestENOSPC(TestErrors):
                 if event['event'] == 'BLOCK_JOB_ERROR':
                     self.assert_qmp(event, 'data/device', 'drive0')
                     self.assert_qmp(event, 'data/operation', 'read')
+                    error = True
 
                     result = self.vm.qmp('query-block-jobs')
                     self.assert_qmp(result, 'return[0]/paused', True)
@@ -676,9 +677,11 @@ class TestENOSPC(TestErrors):
                     self.assert_qmp(result, 'return', {})
 
                     result = self.vm.qmp('query-block-jobs')
+                    if result == {'return': []}:
+                        # Race; likely already finished. Check.
+                        continue
                     self.assert_qmp(result, 'return[0]/paused', False)
                     self.assert_qmp(result, 'return[0]/io-status', 'ok')
-                    error = True
                 elif event['event'] == 'BLOCK_JOB_COMPLETED':
                     self.assertTrue(error, 'job completed unexpectedly')
                     self.assert_qmp(event, 'data/type', 'stream')
@@ -792,13 +795,14 @@ class TestSetSpeed(iotests.QMPTestCase):
 
         self.assert_no_active_block_jobs()
 
+        self.vm.pause_drive('drive0')
         result = self.vm.qmp('block-stream', device='drive0')
         self.assert_qmp(result, 'return', {})
 
         result = self.vm.qmp('block-job-set-speed', device='drive0', speed=-1)
         self.assert_qmp(result, 'error/class', 'GenericError')
 
-        self.cancel_and_wait()
+        self.cancel_and_wait(resume=True)
 
 if __name__ == '__main__':
     iotests.main(supported_fmts=['qcow2', 'qed'])