qa/tasks: drop test_cephadm_orchestrator.py

qa/tasks: drop test_cephadm_orchestrator.py

this test will end with a failure like

```
2020-01-30T18:15:15.870 INFO:tasks.ceph.mgr.x.smithi042.stderr:Warning: Permanently added 'smithi042.front.sepia.ceph.com,172.21.15.42' (ECDSA) to the list of known hosts.
2020-01-30T18:15:15.925 INFO:tasks.ceph.mgr.x.smithi042.stderr:Permission denied, please try again.
2020-01-30T18:15:15.932 INFO:tasks.ceph.mgr.x.smithi042.stderr:Permission denied, please try again.
2020-01-30T18:15:15.939 INFO:tasks.ceph.mgr.x.smithi042.stderr:root@smithi042.front.sepia.ceph.com: Permission denied (publickey,gssapi-keyex,gssapi-with-mic,password).
```

because mgr is not able to establish an ssh connection to that host with "root".
please note, the teuthology worker is acting using the "ubuntu" account on the
test node, and by default, "root" does not have its pubkey. and actually
`qa/tasks/cephadm.py` does push the pubkey to all the managed hosts before
testing cephadm.

since `qa/tasks/cephadm.py` is a better test for cephadm, let's just
drop this one.

as suites/rados/cephadm already covers cephadm

Signed-off-by: Kefu Chai <kchai@redhat.com>