Get the constraints file only when holds a valid value

[freyes]

This change makes the handle-constraints-url validate more aggressively the pip_constraints_url holds a value that can be used, also a new task is introduced to only use the constraints file when its size is larger than zero.

TASK [handle-constraints-url : GET the constraints file]
focal-medium | ERROR
focal-medium | {
focal-medium |   "dest": "/home/ubuntu/constraints.a7h1xj9v.txt",
focal-medium |   "elapsed": 0,
focal-medium |   "gid": 1000,
focal-medium |   "group": "ubuntu",
focal-medium |   "mode": "0600",
focal-medium |   "msg": "An unknown error occurred: a bytes-like object is required, not 'str'",
focal-medium |   "owner": "ubuntu",
focal-medium |   "size": 0,
focal-medium |   "state": "file",
focal-medium |   "uid": 1000,
focal-medium |   "url": null
focal-medium | }