Bug 1658393: Respect group copying rules

When copying (therefore creating) a group owned by an institution
we check if user can edit institution - if not we set institution
to 'mahara'

behatnotneeded

Change-Id: I648d74a70016d4b68e738147cc63952ec8261926
Signed-off-by: Robert Lyon <robertl@catalyst.net.nz>
(cherry picked from commit 0524e220)