CarthageServerRole fails when run from an installed carthage-runner

`copy_in_carthage` setup task calls `rsync_git_tree` on `os.path.dirname(carthage.__file__)` which fails with
```
sh.ErrorReturnCode_128: 

  RAN: /usr/bin/git rev-parse --show-toplevel

  STDOUT:


  STDERR:
fatal: not a git repository (or any of the parent directories): .git
```