install_arch: switch to python3

We've changed ansible to use python3 now and Python 2 will be deprecated
next year.

roles/install_arch/tasks/main.yml

@@ -83,7 +83,7 @@
   command: chroot /tmp/root.x86_64 pacman-key --populate archlinux
 
 - name: install arch base from bootstrap chroot
-  command: chroot /tmp/root.x86_64 pacstrap /mnt base base-devel btrfs-progs grub openssh python2 creates=/tmp/root.x86_64/mnt/bin
+  command: chroot /tmp/root.x86_64 pacstrap /mnt base base-devel btrfs-progs grub openssh python creates=/tmp/root.x86_64/mnt/bin
 
 - name: mount /proc to new chroot
   command: mount --rbind /proc /mnt/proc creates=/mnt/proc/uptime