[QA] naming collisions with normal groups

[jnweiger]

Seen with customgroups-0.7.0-rc.1 and 0.6.2 (not a regression)

• Admin uses '+ add group' on the user account bob to give him a group 'bob-group'.
• Admin navigates to settings -> customgroups and clicks 'create Group' with the same name 'bob-group'. BAD
  • Both groups are distinct objects, e.g. user bob is not member in the second group. OK

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Expected behaviour:

• Existing normal group names cannot be used as custom groups.
• Existing custom groups cannot be used a normal groups.

[jnweiger]

Still seen with 0.9.0-rc.1
One bob-g is a normal group, the other is a custom group:
User has no hint, which is which. BAD.