Refactor clCopyImage and clFillImage tests (#2283)

This change mainly extends `clFillImage` and `clCopyImage` test function
to include memory flags to be used during creating the image instead of
hard-coding these values. The memory flags are also different parameters
for source and destination images in `clCopyImage` tests.

---------

Signed-off-by: Michael Rizkalla <michael.rizkalla@arm.com>

test_common/harness/imageHelpers.h

@@ -126,6 +126,7 @@ typedef struct
     const cl_image_format *format;
     cl_mem buffer;
     cl_mem_object_type type;
+    cl_mem_flags mem_flags;
     cl_uint num_mip_levels;
 } image_descriptor;