Update test_parent_constraints.html

use delay to initialize dojo/dnd/move.parentConstrainedMoveable will get a bug
just modify the test file to show the bug.
do the following step,you will see the bug
1 drag the "moveable1" and mouseup outside the parent dom
2 drag the "moveable1" and mouseup inside the parent dom
3 mouse over the "moveable1"
then you will find the "moveable1" will move together with you mouse without a mousedown.
that is a bug, i think.