title: gcloud composer command fails "executable file not found in $PATH"
body: <p>I am trying to run backfilling an Airflow DAG on Cloud Composer. Am I missing something? </p>
  
  <pre><code>$ gcloud composer environments run myenv \
    --location  us-central1 --project myproject \
    backfill -- -s 2020-10-05T10:30 -e 2020-10-05T10:30 \
    -x -I mydag 
  kubeconfig entry generated for us-central1-myenv-xxx-gke.
  Executing within the following kubectl namespace: xxx
  command terminated with exit code 126
  OCI runtime exec failed: exec failed: container_linux.go:345: starting container process
  caused "exec: \"-s\": executable file not found in $PATH": unknown
  
  ERROR: (gcloud.composer.environments.run) kubectl returned non-zero status code.
  </code></pre>
  
  <p>I am using the following versions of CLI tools.</p>
  
  <pre><code>$ gcloud version
  Google Cloud SDK 286.0.0
  bq 2.0.55
  core 2020.03.24
  gsutil 4.48
  </code></pre>
  
  <p>Composer image version is <code>composer-1.8.3-airflow-1.10.3</code>.</p>
  
  <p>Thank you.</p>