cubicweb-vcsfile #2718635 tests depend on tag and folder cubes: make this optional [done]

for it is very inconvenient

However I don't know how we can make the test/data/bootstrap_cubes thing more flexible.

prioritynormal
typebug
done in1.12.0
load left0.000
closed by#3d6a1a52d7be try to make tag & folder optional (closes #2718635)