Look into getcwd() first when searching for vendor folder

[schlessera]

When the Behat context setup tried to find the vendor folder, it did not look into the current working folder first, instead always finding the vendor folder within the tests dependency instead.

This PR adapts the logic so that the current working directory gets searched first.

As an example, when running composer behat from within the wp-cli-dev/config-command folder, this is the resulting change:

BEFORE

Vendor folder location: /home/alain/dev/wp-cli-dev/wp-cli-tests/vendor
Framework folder location: /home/alain/dev/wp-cli-dev/wp-cli-tests/vendor/wp-cli/wp-cli
WP-CLI binary path: /home/alain/dev/wp-cli-dev/wp-cli-tests/vendor/bin

AFTER

Vendor folder location: /home/alain/dev/wp-cli-dev/config-command/vendor
Framework folder location: /home/alain/dev/wp-cli-dev/config-command/vendor/wp-cli/wp-cli
WP-CLI binary path: /home/alain/dev/wp-cli-dev/config-command/vendor/bin
Project config file location: /tmp/wp-cli-package-test/config.yml
Project config:
require:
  - /home/alain/dev/wp-cli-dev/config-command/config-command.php

The main issue this has caused is that local configuration files used in packages to make sure the current source files are being loaded over any existing package had been ignored.