Mark test_minimum_basic_instance_hard_reboot_after_vol_snap_deletion as slow test

We are seeing more timeout in tests (and so does sometimes it end up to
job timeout) in various jobs. A few examples are

- miltinode job
  - https://zuul.openstack.org/build/084729c5a1fe46e091a17a50441e99d5/log/job-output.txt

- stable/yoga job
  - https://zuul.opendev.org/t/openstack/build/9b79f54d3f6c4e05ae6619fdac7ad95a

Two tests in doubt and taking more time is
test_minimum_basic_instance_hard_reboot_after_vol_snap_deletion
- taking 258.358054s
  - https://zuul.openstack.org/build/084729c5a1fe46e091a17a50441e99d5/log/job-output.txt#34173
- taking 187.411266s
  - https://zuul.opendev.org/t/openstack/build/9b79f54d3f6c4e05ae6619fdac7ad95a/log/job-output.txt#25738

test_minimum_basic_scenario 
- taking 309.109043s
  - https://zuul.opendev.org/t/openstack/build/d068cb494d234fe7b79dc5ae6fd6ae69/log/job-output.txt#24052
  
marking these test as slot test and monitor if there is another slow
test we can find.

Related-Bug: #2004780
Change-Id: I0aff3507b3bf3498ab0ecd548bb57cdcd97ec11a
1 file changed