Refactor the following tests:
1. `test_imagecopy`
2. `test_imagecopy3d`
3. `test_imagereadwrite`
4. `test_imagereadwrite3d`
The change does the following:
1. Use RAII to manage allocated resources
2. For `imagecopy` and `imagecopy3d`, the change allows for a custom src
image memory flags and adjusts how the source image is created according
to the input flags.
Signed-off-by: Michael Rizkalla <michael.rizkalla@arm.com>
