Added exception throwing on test generation if project is not built #61

[vasylmalanka]

Description

Exception throwing has been added to test generation method in order to check if vendor/bin/robo build:project has been ran and .env configuration file has been filled in.

Fixed Issues (if relevant)

1. Validate build:project was run before attempting to generate tests #61: Validate build:project was run before attempting to generate tests

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)
• 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

[magento-cicd2]

All committers have signed the CLA.

[coveralls]

Coverage remained the same at 53.382% when pulling 9763062 on issue-61 into 08c089a on CD-develop.

[okolesnyk]

@vasylmalanka Please fork magento2-functional-testing-framework and make Pull Request from your fork.