High CPU load on x64 dockerhost system

Machine is frequently running with a load of around 60 while the test runs are in progress. The machine has 16 cores. Noting that we have over ten test containers on this system so we may need to revise the CPU caps (and make sure they are working as expected).

We could also look at reducing the priority of the Solaris vagrant machines since that is a low priority platform.

Noting also that the riscv64 builds are running with a particularly high CPU % in the containers:
```
CONTAINER ID NAME CPU % MEM USAGE / LIMIT MEM % NET I/O BLOCK I/O PIDS
36134aa4628d distracted_galois 1176.88% 7.998GiB / 62.79GiB 12.74% 218MB / 515kB 6.38GB / 6.04GB 359
```

Start by examining the Docker test containers on the x64 dockerhost, including their CPU caps and the riscv64 build container's usage. Also review the Solaris Vagrant machines' scheduling priority. Done means the CPU limits behave as intended and the test workload no longer drives excessive host load.

Written by the indexing model from the issue text.