builder: Fix virt-builder test.

Add Europe/London timezone to phony Fedora guest.

This fixes commit dd1bfea513658368afd3728e0c5bf8ab6041cd1f.
builder/website: Add CirrOS signature file to EXTRA_DIST.

This fixes commit 40b88fdbc76515fd21b33f54587c7f4f7b6e9715.
Version 1.25.20.