tests: Add regex-based ignore rules for ref files

tests: Add regex-based ignore rules for ref files

There are cases where we need to ignore files with specific extensions
(e.g., when Mercurial litters the file system with patch
rejects). Implement this functionality using a helper class
(FileIgnoreList) that supports both regular expressions and basic
string comparisons.

Change-Id: I34549754bd2e10ed230ffb2dc057403349f8fa78
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>