Various provision fixes
This series addresses various provision issues that we encountered in upstream libvirt CI:
- raises the SSH wait timeout to conservative 60s as multiple concurrent machines asking DHCP for an IP address at the same time can easily grow over the 30s limit
- ECONNREFUSED added to the list of errnos we ignore during the provisioning time frame
- provisioner's exception handler was split in 2 because the exceptions have a common parent and hence the handling of them needs to be distinct to each otherwise the more generic exception type always wins
- work around virt-install's concurrent 'boot-scratch' storage pool refresh (see the patch)
Many test executions have been run with these patches, a sample libvirt CI pipeline: https://gitlab.com/eskultety/libvirt/-/pipelines/798751522