Some packages may require additional group membership for the system
user added by that package. Allow defining additional groups as third
member of the ':'-separated tuple, allowing to specify multiple
','-separated groups with optional GID.
Example:
USERID:=foouser=1000:foogroup=1000:addg1=1001,addg2=1002,addg3
Signed-off-by: Daniel Golle <daniel@makrotopia.org>
b2aca61360