Continuous buildfarm failures on hamster with bin-check

Hi all,

Some of you may have noticed that hamster is heavily red on the
buildfarm. I have done a bit of investigation, and I am able to
reproduce the failure manually. But actually after looking at the logs
the error has obviously showed up:
2017-04-16 05:07:19.650 JST [18282] LOG: database system is ready to
accept connections
2017-04-16 05:08:36.725 JST [18296] LOG: using stale statistics
instead of current ones because stats collector is not responding
2017-04-16 05:10:22.207 JST [18303] t/010_pg_basebackup.pl LOG:
terminating walsender process due to replication timeout
2017-04-16 05:10:30.180 JST [18306] LOG: using stale statistics
instead of current ones because stats collector is not responding

Stale regressions means that the system is just constrained so much
that things are timing out.

In order to avoid such failures with normal regression tests, I have
set up extra_config so as stats_temp_directory goes to a tmpfs to
avoid stale statistics, but it is not possible to set up that with the
TAP tests. I could always disable --enable-tap-tests on this machine
but I don't think that this is a correct answer. Something that could
be done is to use an environment variable to set up a base directory
for all the nodes created in PostgresNode.pm, and use that for
temporary statistics with a custom folder name. But that's not
scalable if we want to enforce more parameter.

Thoughts?
--
Michael