[MINOR] acl: ignore empty lines and comments in pattern files

[MINOR] acl: ignore empty lines and comments in pattern files

Most often, pattern files used by ACLs will be produced by tools
which emit some comments (eg: geolocation lists). It's very annoying
to have to clean the files before using them, and it does not make
much sense to be able to support patterns we already can't input in
the config file. So this patch makes the pattern file loader skip
lines beginning with a sharp and the empty ones, and strips leading
spaces and tabs.