Proper check for empty response in autoscaling test

searching for literal "[]" string to check for no entities in response
is brittle, as the returned JSON of entities may include empty list
as a value for some properties.

Instead, use proper json path search and comparison.

Related-Issue: PRODX-54144
Change-Id: I85b89b748d663fd1f71fb96055066cae7f42879f
1 file changed