Use {{ ansible_pkg_mgr }} instead of yum

This should make things work on systems with dnf and even on systems
which use apt!

contrib/ansible/roles/etcd/tasks/main.yml

@@ -1,6 +1,9 @@
 ---
 - name: Install etcd
-  yum: pkg=etcd state=latest
+  action: "{{ ansible_pkg_mgr }}"
+  args:
+        name: etcd
+        state: latest
   notify:
         - restart etcd
   when: not is_atomic

contrib/ansible/roles/kubernetes/tasks/main.yml

@@ -3,7 +3,10 @@
   when: ansible_distribution == "Fedora"
 
 - name: Install kubernetes
-  yum: pkg=kubernetes state=latest
+  action: "{{ ansible_pkg_mgr }}"
+  args:
+        name: kubernetes
+        state: latest
   notify:
         - restart daemons
   when: not is_atomic