Toolbar overrides: don't overwrite existing groups
Toolbar overrides: don't overwrite existing groups

Right now, a plugin toolbar override can replace entire ui-classic button groups by accidentally using the same name.
If multiple plugins do that for the same entity, a random plugin would win.

By prefixing button group ids for groups from plugins, each plugin gets a unique namespace within the toolbar,
so it can still add selects and buttons, just not replace existing ones.

(I would like to solve the labeling clashes too, but I don't see a way of doing "class.source_engine",
so without guessing from the class name, or explicitly adding the name in each override, I don't see a nice way,
so we may need to solve it plugin-side.)

ManageIQ/manageiq-ui-classic,ManageIQ/manageiq-ui-classic,ManageIQ/manageiq-ui-classic,ManageIQ/manageiq-ui-classic