Reallow project paths ending in periods
While reviewing https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/15135, I realized that we accidentally started treating project paths ending in . as invalid, while they should have been valid!
This bug was introduced in https://gitlab.com/gitlab-org/gitlab-ce/commit/bccf8d86c57a141aeb60d96bc3139fe2b5dc9240, when we started validating the project path using the namespace format regex.
By fixing this bug, we effectively resolve https://gitlab.com/gitlab-org/gitlab-ce/issues/39695, and replace https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/15135.