Build fstrim in util-linux (and maybe update to newer version) #532

Our version of util-linux is ancient (e.g. fdisk still creates partitions at odd LBA addresses), and has fstrim disabled, probably due to limitations of the old 4.9 kernel. This caused a strange, disk-related slowdown for me while bootstrapping Azure Linux on top of live-bootstrap, which turned out to be due to TRIM not being used.

We should try to reenable fstrim now that we have a newer kernel, and maybe even update to a version of util-linux that's more SSD-friendly.