Deal with missing wiki repositories
Currently, every GitLab project has an accompanying wiki repository. In the past, the wiki repository was created only on demand.
When copying gitlab.com data around it bites us that there are over 10,000 projects created in the time when wiki's were created on demand: it means that we have to sift through over 10,000 '/foo/bar.wiki.git No such file or directory' errors all the time.
I think we should have a rake task that can initialize the missing wiki repositories.