Small fixes:
- spread.yaml: adding more workers for ubuntu 20.04
- packaging: stop depending on python-docutils on opensuse
- spread.yaml: do not run ubuntu-core-20-64 with snapd 2.44, snapd is not recent enough to drive ubuntu-core-20
- spread.yaml: Preserve size for centos images on spread.yaml
- spread.yaml: use non-uefi enabled image for uc20
- tests: ensure $cache_dir is actually available
- tests: disable preseed tests, they work in master but require too much cherry-picking here
- travis.yml: remove go/master unit tests from 2.44
- packaging/fedora: disable FIPS compliant crypto for static binaries
- interfaces/firewall-control: allow -legacy and -nft for core20
- seccomp: add get_tls, io_pg* and *time64/*64 variants for existing syscalls
- tests: 16.04 and 18.04 now have mediating pulseaudio
- tests: ignore user@12345.service hierarchy