Fix where instance filter failed if matched with more than one item by regex

```
$ kitchen list
Instance                      Driver   Provisioner  Last Action
gdb01-master-ubuntu-1204      Vagrant  ChefSolo     Created
logdb01-master-ubuntu-1204    Vagrant  ChefSolo     Created

$ kitchen login gdb01-master-ubuntu-1204
>>>>>>
Argument `gdb01-master-ubuntu-1204' returned multiple results:
  * gdb01-master-ubuntu-1204
  * logdb01-master-ubuntu-1204
  
```