mgr: add a check task for all mgr to be up

mgr: add a check task for all mgr to be up

This can't be backported from master since there was too many
modifications meantime.

When mgr aren't all ready, sometimes the following error can show up:

```
stderr: 'Error ENOENT: all mgr daemons do not support module ''status'', pass --force to force enablement'
```

This commit adds a check so all mgr are available when we try to enable
modules.

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