Projects::ForkService delegates to this service almost entirely, but needed
one small change so it would propagate create errors correctly.
CreateService#execute needs significant refactoring; it is now right at the
complexity limit set by Rubocop. I avoided doing so in this commit to keep the
diff as small as possible.
Several tests depend on the insecure behaviour of ForkService, so fi them up at
the same time.
Add gitlab-shell to error message to give user a clue that something may be wrong there.
Ran into this in #2082. User was told that repositories were created when they were
not due to hooks symlink being wrong.
Remove overload of BaseService.initialize, so initialize gains params,
which is used to pass the namespace (like e.g. in TransferService).
The namespace is checked for permission to create projects in it.
