Trying to clone a repository that is not in our routing table returns an error:

``` (fail)
$ rad clone rad:zVNuptPuk5XauitpCWSNVCXGGfXW --scope followed
✓ Seeding policy updated for rad:zVNuptPuk5XauitpCWSNVCXGGfXW with scope 'followed'
✗ Error: fetch: no candidate seeds were found to fetch from
```