Mftf 877 missed php variables

[asannikov]

MagentoWebDriverDoctor uses wrong variables for webdriver_proxy definition.

Description

Fixed variable names in MagentoWebDriverDoctor

Fixed Issues (if relevant)

1. mftf doctor produces php notices because of missed variables #877: mftf doctor produces php notices because of missed variables2.

Contribution checklist

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/verification tests (if applicable)
• [x ] All automated tests passed successfully (all builds on Travis CI are green)
• Changes to Framework doesn't have backward incompatible changes for tests or have related Pull Request with fixes to tests