[#1150] Read the benchmark JTL with a CSV parser, so that an error whose message holds a comma reaches the step log

[vharseko]

Fixes #1150

Problem

compare-opendj.sh listed the errors of each benchmark side with awk -F','. JMeter quotes a responseMessage
that contains a comma, and every message naming a DN does, so the columns after it shifted and such rows were
never matched as failures. On the PDB side this hid the result-80 and result-32 rows of #1149 and left only
BIND | 49, the last consequence of a failed ADD.

Change

The error listing in bench_one now reads the JTL with python3's csv module, which is already used by the
same Docker jobs in build.yml.

• Failures are grouped by operation, result code and message, with digits in the message replaced by N. The
  messages carry the entry DN or the elapsed milliseconds, and without this each failed row would be a kind of its
  own.
• The step log shows the number of failed rows and kinds of error, the ten most frequent kinds and, when there are
  more, how many are left out.
• The listing still goes to stderr, because stdout of bench_one carries the server version. || true keeps a
  failure of the listing from stopping the benchmark.

The err columns of the step summary come from statistics.json through summary.sh and are unchanged.

Verification

The block, cut verbatim from the script, run on the benchmark-pdb-vs-je artifacts named in the issue:

JTL	Before (awk)	After
36845050319, PDB	2 BIND | 49	12 failed rows, 6 kinds of error: DELETE/ADD/READD 80, COMPARE/MODIFY 32, BIND 49
36738515054, PDB	5131 BIND | 800, 2 BIND | 49	5145 failed rows, 7 kinds of error, with the 80 and 32 rows present
JE side and both build-vs-release runs	nothing	nothing (no failed rows)

Output for run 36845050319, PDB:

[b] 12 failed rows, 6 kinds of error (count | op | code | message):
      3 DELETE | 80 | pdb: backend 'userRoot' did not apply the transaction after N attempts in N ms, the attempt cap being spent; the last conflict was com.persistit.exception.RollbackException
      2 ADD | 80 | pdb: backend 'userRoot' did not apply the transaction after N attempts in N ms, the attempt cap being spent; the last conflict was com.persistit.exception.RollbackException
      2 COMPARE | 32 | The specified entry mail=u_N_N@test.com,ou=People,dc=example,dc=com does not exist in the Directory Server
      2 MODIFY | 32 | Entry mail=u_N_N@test.com,ou=People,dc=example,dc=com cannot be modified because no such entry exists in the server
      2 BIND | 49 | Invalid Credentials
      1 READD | 80 | pdb: backend 'userRoot' did not apply the transaction after N attempts in N ms, the attempt cap being spent; the last conflict was com.persistit.exception.RollbackException

A synthetic JTL with 13 kinds of error, messages holding commas and one message spanning two lines printed ten
kinds and ... 3 more kinds not shown. When the JTL is missing or malformed, the block exits with 0. In every case
nothing was written to stdout. bash -n passes.

#1145 edits the same file in a different place (the sysctl near the top), so the two do not conflict.