"Address already in use" on CI when building parity-ethereum

[ddorgan]

Before filing a new issue, please provide the following information.

• Parity Ethereum version: all current builds
• Operating system: Linux
• Installation: N/A
• Fully synchronized: n/a
• Network: n/a
• Restarted: n/a

From dvdplm:

I had an issue today with a spurious test failure. I restarted the job and it completed fine (no code changes).
https://gitlab.parity.io/parity/parity-ethereum/-/jobs/103008 – Failed with: Error(Io(Os { code: 98, kind: AddrInUse, message: "Address already in use" }),
Restarting worked:
https://gitlab.parity.io/parity/parity-ethereum/-/jobs/103096

Both were executed on the same host, hopefully not due to parallel testing in one container.