cubicweb #2544454 add_cube misbehavior [open]

test case:
create an instance from the 'forge' cube
run add_cube('apycot')
notice that the cw_testexecution sql table is missing the cw_execution_of column

creating an instance from a dedicated cube with dependencies on forge+apycot works around this.

prioritynormal
typebug
done in<not specified>
closed by<not specified>