Extract helper from merge_wildcard_linter_options

This method was complex. Simplify it a bit by extracting a helper
method `linter_names_matching_glob`.

Change-Id: I4bede82fb4fc64041576055d34246fefac5efb4a
Reviewed-on: http://gerrit.causes.com/44955
Tested-by: jenkins <jenkins@brigade.com>
Reviewed-by: Shane da Silva <shane.dasilva@brigade.com>