Check that OPSI is fully working on groups

OPSI tab is available on object groups of workstations, we should make sure that this is fully functional.

(from redmine: issue id 5506, created on 2017-05-02, closed on 2017-05-30)

• Changesets:
  • Revision 485c959e by Côme Chilliet on 2017-05-02T13:22:28.000Z:

Fixes #5506 fixing PHP errors on OPSI tab

• Revision bcd21f56 by Côme Chilliet on 2017-05-02T13:27:39.000Z:

Fixes #5506 fixing PHP errors on OPSI tab

• Revision c464e5e9 by Côme Chilliet on 2017-05-04T12:38:09.000Z:

Fixes #5506 Avoid showing errors when members have their own OPSI tab active

Polished errors a bit too

• Custom Fields:
  • Support contract: None
  • Dolibarr project Name: PJ1703-0080