Several improvements on behat context

| Q                    | A
| -------------------- | ---
| Bug fix?             | no
| New feature?         | no
| BC breaks?           | no
| CI currently passes? | yes
| Tests pass?          | yes
| Scenarios pass?      | yes
| Checkstyle issues?   | no
| Changelog updated?   | no
| Fixed tickets        |
| Doc PR               |

- Be able to create a single product like that:

``` gherkin
Given the following product:
| SKU        | shoe  |
| families   | shoes |
| name-en_US | foo   |
```

- Improve step exceptions
- Improve field icons retrieval
- Check value of a field using `Then the field english Name should contain "foo"`
- Correctly check value of an upload file widget