Added stdout redirection

When Cucumber tests produce content in stdout, such as debug
information, multicuke records this information in a file named after
the test being run.

For instance, "bad_addition" test will now produce two files :
- results/cucumber_reports/bad_addition.html - The cucumber report
- results/cucumber_reports/bad_addition.stdout - The console output

Note that this does not work for stderr, consider migrating to
Open3::popen3 in case this is needed.