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

``` (fail)
$ rad clone rad:zVNuptPuk5XauitpCWSNVCXGGfXW --scope trusted
✓ Tracking relationship established for rad:zVNuptPuk5XauitpCWSNVCXGGfXW with scope 'trusted'
✗ Error: no seeds found for rad:zVNuptPuk5XauitpCWSNVCXGGfXW
```