Delete job working directory if it already exists

.gitignore

@@ -1 +1,2 @@
 runner.toml
+run

runner/runner.go

@@ -30,7 +30,12 @@ func RunJob(job Job, workingDir string) error {
 
 	log.Debugf("Job %v configured with folder \"%v\"", job.Id, jobFolder)
 
-	err := os.MkdirAll(jobFolder, 0755)
+	err := os.RemoveAll(jobFolder)
+	if err != nil {
+		return fmt.Errorf("could not delete existing folder %v", jobFolder)
+	}
+
+	err = os.MkdirAll(jobFolder, 0755)
 	if err != nil {
 		return fmt.Errorf("could not create working directory for job %v: %v", job.Id, err)
 	}