Make the 'cucumber' compilation pattern work without 'omake'

Make the 'cucumber' compilation pattern work without 'omake'

When 'omake' is included in compilation-error-regexp-alist, which it
still is by default, then all other rules are modified to match with
an extra leading 6 spaces as well. The 'cucumber' pattern relied on
this in order to work as intended.

* lisp/progmodes/compile.el (compilation-error-regexp-alist-alist):
Extend the 'cucumber' pattern so that it works even when 'omake'
is not included.  Move it below the 'gnu' rule so that it doesn't
match anything else.