Add CentOS (#12)

* Add CentOS 7

* Fix rawhide boot

* Test locale versions

distros/centos-8stream-x86_64.pkrvars.hcl.sh

@@ -0,0 +1,24 @@
+#!/usr/bin/env bash
+
+# Name of the file to write out
+name="${0%.sh}"
+
+checksums="$(mktemp)"
+until curl -f -L -o "${checksums}" "http://mirror.centos.org/centos/8-stream/isos/x86_64/CHECKSUM"; do
+	sleep 1
+done
+sha="$(cat "${checksums}" | grep latest-boot | grep SHA256 | cut -d' ' -f 4)"
+
+cat << EOF > "${name}"
+distro = "centos"
+version = "8stream"
+iso = {
+	url = "http://mirror.centos.org/centos/8-stream/isos/x86_64/CentOS-Stream-8-x86_64-latest-boot.iso"
+	checksum = "${sha}"
+}
+boot_command = [
+  "<esc><wait>",
+  "linux net.ifnames=0 biosdevnames=0 inst.ks=http://{{.HTTPIP}}:{{.HTTPPort}}/centos/8stream/x86_64.ks console=ttyS0",
+  "<enter>"
+]
+EOF