Use var for bin dir instead of assuming /usr/local/bin

On CoreOS the binaries are not installed in /usr/local/bin.

roles/dnsmasq/tasks/main.yml

@@ -43,7 +43,7 @@
   kube:
     name: dnsmasq
     namespace: kube-system
-    kubectl: /usr/local/bin/kubectl
+    kubectl: "{{bin_dir}}/kubectl"
     resource: "{{item.item.type}}"
     filename: /etc/kubernetes/{{item.item.file}}
     state: "{{item.changed | ternary('latest','present') }}"