bin/tests/system/start.pl improperly detects server startup after all servers are restarted

bin/tests/system/start.pl waits until a running message is logged by a given name server instance before attempting to send a version.bind/CH/TXT query to it. The idea behind this was to make the script wait until named loads all the zones it is configured to serve before telling the system test framework that a given server is ready to use; this prevents the need to add boilerplate code that waits for a specific zone to be loaded to each test expecting that.

However, when looking for running messages, bin/tests/system/start.pl assumes that the existence of any such message in the named.run file means that a given instance has finished loading all zones. Meanwhile, some system tests restart all the server instances throughout their lifetime (some even do that a few times), for example to run Python-based tests. bin/tests/system/start.pl handles such a scenario incorrectly - as soon as it finds any running message in the named.run file it inspects and it gets a response to a version.bind/CH/TXT query, it tells the system test framework that a given server is ready to use, which might not be true - it is possible that only the version.bind zone has been loaded at that point and the running message was logged by a previously-shutdown named instance. This triggers intermittent failures for Python-based tests, e.g.:

https://gitlab.isc.org/isc-private/bind9/-/jobs/2819525

D:doth:        # Check whether a response was received and whether it is sane.
D:doth:        assert response
D:doth:        assert query.id == response.id
D:doth:>       assert len(response.answer) == 1
D:doth:E       assert 0 == 1
D:doth:E         +0
D:doth:E         -1
D:doth:
D:doth:tests_gnutls.py:102: AssertionError

In this case, the response received was a SERVFAIL response (while a NOERROR response was expected):

10-Oct-2022 08:08:10.578 TLS server session created for 10.53.0.1#36440 on 10.53.0.1#9042
10-Oct-2022 08:08:10.578 clientmgr @0x7b2000014100 attach: 2
10-Oct-2022 08:08:10.578 query client=0x7b7c00030368 thread=0x7f6305f7b640(<unknown-query>): query_reset
10-Oct-2022 08:08:10.578 client @0x7b7c00030368 (no-peer): allocate new client
10-Oct-2022 08:08:10.578 client @0x7b7c00030368 10.53.0.1#36440: TCP request
10-Oct-2022 08:08:10.578 client @0x7b7c00030368 10.53.0.1#36440: using view '_default'
10-Oct-2022 08:08:10.578 client @0x7b7c00030368 10.53.0.1#36440: request is not signed
10-Oct-2022 08:08:10.578 client @0x7b7c00030368 10.53.0.1#36440: recursion not available (recursion not enabled for view)
10-Oct-2022 08:08:10.578 query client=0x7b7c00030368 thread=0x7f6305f7b640(<unknown-query>): ns_query_start
10-Oct-2022 08:08:10.578 query client=0x7b7c00030368 thread=0x7f6305f7b640(example/SOA): qctx_init
10-Oct-2022 08:08:10.578 query client=0x7b7c00030368 thread=0x7f6305f7b640(example/SOA): client attr:0x20001, query attr:0x700, restarts:0, origqname:example, timer:0, authdb:0, referral:0
10-Oct-2022 08:08:10.578 query client=0x7b7c00030368 thread=0x7f6305f7b640(example/SOA): ns__query_start
10-Oct-2022 08:08:10.578 query client=0x7b7c00030368 thread=0x7f6305f7b640(example/SOA): ns__query_start: query_getdb failed
10-Oct-2022 08:08:10.578 query client=0x7b7c00030368 thread=0x7f6305f7b640(example/SOA): ns_query_done
10-Oct-2022 08:08:10.578 client @0x7b7c00030368 10.53.0.1#36440 (example): query failed (zone not loaded) for example/IN/SOA at query.c:5644
10-Oct-2022 08:08:10.578 client @0x7b7c00030368 10.53.0.1#36440 (example): reset client
10-Oct-2022 08:08:10.578 query client=0x7b7c00030368 thread=0x7f6305f7b640(example/SOA): query_reset
10-Oct-2022 08:08:10.578 client @0x7b7c00030368 10.53.0.1#36440: freeing client
10-Oct-2022 08:08:10.578 query client=0x7b7c00030368 thread=0x7f6305f7b640(<unknown-query>): query_reset
...
10-Oct-2022 08:08:10.726 zone example/IN: loaded serial 1397051952