selftests/bpf: Fix flavored variants of test_ima

Flavored variants of test_progs (e.g. test_progs-no_alu32) change their
working directory to the corresponding subdirectory (e.g. no_alu32).
Since the setup script required by test_ima (ima_setup.sh) is not
mentioned in the dependencies, it does not get copied to these
subdirectories and causes flavored variants of test_ima to fail.

Adding the script to TRUNNER_EXTRA_FILES ensures that the file is also
copied to the subdirectories for the flavored variants of test_progs.

Fixes: 34b82d3a ("bpf: Add a selftest for bpf_ima_inode_hash")
Reported-by: Yonghong Song <yhs@fb.com>
Suggested-by: Yonghong Song <yhs@fb.com>
Signed-off-by: KP Singh <kpsingh@google.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20201126184946.1708213-1-kpsingh@chromium.org