Correct is_test_from_kernel_xml if input xml not exist

The original logic for is_test_from_kernel_xml will raise exception if
input xml not exist but it will lead to the problem for the rest logic
for find_test_by_module_and_class() not be run completele. Change the
logic to return False instead.

Bug: 202764540
Test: m clean; atest-src cow_api_test:cow_api_test.CowTest#ResumeSeqOp -c
Change-Id: I9fd06a43ccf2e9ae95560314d928974eed311b27