KVM: selftests: Print a more helpful message for EACCESS in access tracking test

Use open_path_or_exit() helper to probe /sys/kernel/mm/page_idle/bitmap in
the access tracking perf test so that a helpful/pertinent SKIP message is
printed if the file exists but is inaccessible, e.g. because the file has
the kernel's default 0600 permissions.

Cc: James Houghton <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Sean Christopherson <[email protected]>

Author: sean-jc

tools/testing/selftests/kvm/access_tracking_perf_test.c

@@ -596,11 +596,8 @@ int main(int argc, char *argv[])
 		if (ret)
 			return ret;
 	} else {
-		page_idle_fd = open("/sys/kernel/mm/page_idle/bitmap", O_RDWR);
-		__TEST_REQUIRE(page_idle_fd >= 0,
-			       "Couldn't open /sys/kernel/mm/page_idle/bitmap. "
-			       "Is CONFIG_IDLE_PAGE_TRACKING enabled?");
-
+		page_idle_fd = __open_path_or_exit("/sys/kernel/mm/page_idle/bitmap", O_RDWR,
+						   "Is CONFIG_IDLE_PAGE_TRACKING enabled?");
 		close(page_idle_fd);
 
 		puts("Using page_idle for aging");