fate: disable globbing when calling shell functions.

Some of the filters tests use globbing characters, especially
brackets for filter pad labels. While most of these strings
are way too complicated to ever match an existing file name
and are therefore kept unchanged in the command line (an old
misfeature of the shell language that happens to be convenient
here), at least one use is simple enough to match random files
lying in the current directory. If that happens, the string,
that was meant to be kept verbatim, is replaced by the file
name, and that causes the test to fail (or worse).