use command module instead of shell module

roles/etcd/tasks/gen_certs_script.yml

@@ -115,7 +115,7 @@
 
 # FIXME(mattymo): Use tempfile module in ansible 2.3
 - name: Gen_certs | Prepare tempfile for unpacking certs
-  shell: mktemp /tmp/certsXXXXX.tar.gz
+  command: mktemp /tmp/certsXXXXX.tar.gz
   register: cert_tempfile
   when: inventory_hostname in groups['etcd'] and sync_certs|default(false) and
         inventory_hostname != groups['etcd'][0]

roles/kubernetes/secrets/tasks/gen_certs_script.yml

@@ -117,7 +117,7 @@
 
 # FIXME(mattymo): Use tempfile module in ansible 2.3
 - name: Gen_certs | Prepare tempfile for unpacking certs
-  shell: mktemp /tmp/certsXXXXX.tar.gz
+  command: mktemp /tmp/certsXXXXX.tar.gz
   register: cert_tempfile
   when: inventory_hostname in groups['kube-master'] and sync_certs|default(false) and
         inventory_hostname != groups['kube-master'][0]