After f613a7c4 ("pkg/cover: fix prefix computation") we stopped trimming
starting "/" from linux path names. This broke get_maintainers.pl script
which is now given non-existent absolute paths (e.g. "/mm/mmap.c"),
as the result syzbot can't find any maintainers for bug reports
and mails them into lkml limbo.
Trim starting slashes and dots. Extend tests for catch this.
We now pass 5 arguments through a bunch of functions,
this is quite inconvinient when the set of arguments changes.
Incapsulate all arguments in a struct and pass/store it as a whole.
