And hence, congestion with possible timeouts on resource.

Fixes apache#1609

self-assigned this

cstamas changed the title GH-1609 Bad metadata naming cause name colllaps GH-1609 Bad metadata naming

Lock names by def should be flat, not follow same layout
as local repo paths.

We already had means to "make sure string is valid for path segment",
but it was buried in RepositoryIdHelper.

Pull it out, and make it reusable, as this is essentially very
same use case. Also, the "expensive" method really punishes
ONLY non maven metadata, and those should be few only.