Avoid unnecesary task creation for slicing arrays

[salvisolamartinell]

Describe the bug Slicing a ds-array creates unnecessary tasks when the slice matches with the blocks.

To Reproduce No details available.

Expected behavior Ds-array slicing shouldn't create unnecessary tasks.

Environment (please complete the following information):

• COMPSs version: 2.8
• Dislib version: 0.6.4

Additional context This has been reported in a program using utils.shuffle(x,y) + _paired_partition(x,y). _paired_partition creates unnecessary tasks.

Related: avoid sending the inner blocks to a task when slicing an array.