Fix upgrader for Ubuntu 18.04

Ubuntu 18.04 has ansible 2.5. In this version get_md5 changed default
from yes to no (see
https://docs.ansible.com/ansible/latest/modules/stat_module.html)

Warning: this optionwill be removed totally in Ansible 2.9.

playbook/roles/upgrader/tasks/main.yml

@@ -37,7 +37,9 @@
     when: hosts_file.stat.exists == True
 
   - name: Save new archive MD5
-    stat: path=/opt/upgrader/archive.tar.gz
+    stat:
+      path=/opt/upgrader/archive.tar.gz
+      get_md5=yes
     register:
       archive
 

playbook/roles/vm-bootstrap/tasks/upgrader.yml

@@ -19,7 +19,9 @@
     shell: slapcache-download --destination=/opt/upgrader/archive.tar.gz
 
   - name: Save new archive MD5
-    stat: path=/opt/upgrader/archive.tar.gz
+    stat:
+      path=/opt/upgrader/archive.tar.gz
+      get_md5=yes
     register: archive
 
   - name: Update playbook md5