dashboard: fix timeout usage on rgw user creation command
dashboard: fix timeout usage on rgw user creation command

For some reason, this is making the playbook failing like following:

```
TASK [ceph-dashboard : create radosgw system user] ************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************
task path: /home/guits/ceph-ansible/roles/ceph-dashboard/tasks/configure_dashboard.yml:106
Tuesday 30 July 2019  10:04:54 +0200 (0:00:01.910)       0:11:22.319 **********
FAILED - RETRYING: create radosgw system user (3 retries left).
FAILED - RETRYING: create radosgw system user (2 retries left).
FAILED - RETRYING: create radosgw system user (1 retries left).
fatal: [mgr0 -> mon0]: FAILED! => changed=true
  attempts: 3
  cmd: timeout 20 podman exec ceph-mon-mon0 radosgw-admin user create --uid=ceph-dashboard --display-name='Ceph dashboard' --system
  delta: '0:00:20.021973'
  end: '2019-07-30 08:06:32.656066'
  msg: non-zero return code
  rc: 124
  start: '2019-07-30 08:06:12.634093'
  stderr: 'exec failed: container_linux.go:336: starting container process caused "process_linux.go:82: copying bootstrap data to pipe caused \"write init-p: broken pipe\""'
  stderr_lines: <omitted>
  stdout: ''
  stdout_lines: <omitted>
```

using `timeout -f -s KILL` fixes this issue.

Also, there is no need to use `shell` module here, let's switch to
`command`.

Signed-off-by: Guillaume Abrioux <30a9df5a0293a6108675377fa1673f7aa713f915@redhat.com>

ceph/ceph-ansible,ceph/ceph-ansible