scripts/tester_install.sh

This adds a new script for installing a base OS on CI testers, with configuration to support CI bootstrapping by ansible. The base OS is Arch Linux. The script is meant to be run from an (unmodified) Arch Linux installation media ISO by: # curl http://server/tester_install.sh |bash

The only user input required is entering the hostname. SSH, NTP, and networking are all configured by the script. It should automatically detect the boot mode (BIOS vs UEFI) and install the correct bootloader.

For the root disk, it select the first non-mounted physical block device.

I've tested this quite bit in a VM (both with UEFI and BIOS boot), and tested an earlier version of this script on a system in the CI lab last year (that experiment ultimately failed because everything relies on Saltstack, so it was no fault of this installer)

The installer passes shellcheck, with some exceptions (see commented shellcheck exceptions in the script).