mgr: wait for all mgr to be available

mgr: wait for all mgr to be available

before managing mgr modules, we must ensure all mgr are available
otherwise we can hit failure like following:

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

It happens because all mgr are not yet available when trying to manage
with mgr modules.

Closes: #3100
Signed-off-by: Guillaume Abrioux <gabrioux@redhat.com>