tests: convert several tests from match_grep to match_diff

tests: convert several tests from match_grep to match_diff

* tests/sendfile.test: Use match_diff instead of match_grep.
* tests/sendfile64.test: Likewise.
* tests/time.test: Likewise.
* tests/utime.test: Likewise.
* tests/xet_robust_list.test: Likewise.
* tests/sendfile.c (main): Update match patterns for match_diff.
* tests/sendfile64.c (main): Likewise.
* tests/time.c (main): Likewise.
* tests/utime.c (main): Likewise.
* tests/xet_robust_list.c (main): Likewise.