* Enable customization of supermarket_url
It looks like this was originally supposed to work, but at some point
the default value was put in the method body rather than in the method
parameters.
This change allows you to configure the supermarket_url in test kitchen
like so:
```
verifier:
inspec_tests:
- name: linux-hardening
supermarket: som3guy/apache-disa-stig
supermarket_url: https://my.supermarket.com
```
Signed-off-by: Ryan Larson <ryan.mango.larson@gmail.com>
