Selftests had to run sequentially

[jimklimov]

When preparing Jenkinsfile integration, some tests failed if several runs in the same operating environment happened simultaneously. Job had to be marked sequential=1.

Revise if this is still valid, fix whatever is offending (if still valid).

Probable offenders can include hardcoded fixed port numbers, file names (including unix domain sockets, IPC, etc.) or agent names on the stream - so several processes might collide, steal each others responses, etc. unexpectedly for current selftest code.

[bluca]

I thought we fixed them all? There were no IPC and all TCP bind are dynamic now iirc

[jimklimov]

I did not have time to dig deeper into the why's - just noticed that empirically tests done in parallel tended to fail recently. At least, a reminder to myself to retest if this is still a real issue; if not, can make tests parallel again :\ Either way, actionable issue ;)