perf test trace: Remove set -e for BTF general tests

Remove set -e and print error messages in BTF general tests.

Before:
    $ sudo /tmp/perf test btf -vv
    108: perf trace BTF general tests:
    108: perf trace BTF general tests                                    : Running
    --- start ---
    test child forked, pid 889299
    Checking if vmlinux BTF exists
    Testing perf trace's string augmentation
    String augmentation test failed
    ---- end(-1) ----
    108: perf trace BTF general tests                                    : FAILED!

After:
    $ sudo /tmp/perf test btf -vv
    108: perf trace BTF general tests:
    108: perf trace BTF general tests                                    : Running
    --- start ---
    test child forked, pid 886551
    Checking if vmlinux BTF exists
    Testing perf trace's string augmentation
    String augmentation test failed, output:
    :886566/886566 renameat2(CWD, "/tmp/file1_RcMa", CWD, "/tmp/file2_RcMa", NOREPLACE) = 0---- end(-1) ----
    108: perf trace BTF general tests                                    : FAILED!

Signed-off-by: Howard Chu <howardchu95@gmail.com>
Tested-by: Namhyung Kim <namhyung@kernel.org>
Link: https://lore.kernel.org/r/20250528191148.89118-5-howardchu95@gmail.com


Signed-off-by: Namhyung Kim <namhyung@kernel.org>