Allow OCR-only needles
os-autoinst requires all needles to include at least one match area (in
needle.pm). This seems an arbitrary requirement, which prevents the use of OCR-only needles. This is a bit of a problem for me right now as I could really do with using an OCR-only needle for a 'clean GNOME desktop' match - Fedora Rawhide now has the new translucent top bar in GNOME, and uses a background which changes with the time of day, which means there's not a single entirely predictable pixel on a clean GNOME desktop in Rawhide, which makes using a needle with a match area...difficult.