Replace error-prone `create_random_data` with a reliable implementation

[MichaelRizkalla-arm]

create_random_data is an error-prone function that returns a pointer to allocated memory using malloc.

As mentioned in #2177:

we really ought to remove use of the create_random_data function entirely given that it's so error-prone. This shouldn't be too bad, since there are only a dozen or so places where create_random_data is called, and about half of the uses are in these two files.