Powershell: check exit code in writeCommandChecked
Powershell: check exit code in writeCommandChecked

fixes #81

ayufan/gitlab-ci-multi-runner,hu19891110/gitlab-ci-multi-runner,soiff/gitlab-ci-multi-runner,hu19891110/gitlab-ci-multi-runner,ayufan/gitlab-ci-multi-runner,hu19891110/gitlab-ci-multi-runner,ayufan/gitlab-ci-multi-runner,soiff/gitlab-ci-multi-runner,soiff/gitlab-ci-multi-runner