zabbix: add prerequisites for snmp features for zabbix

zabbix-server/files/snmp.conf

+#
+# As the snmp packages come without MIB files due to license reasons, loading
+# of MIBs is disabled by default. If you added the MIBs you can reenable
+# loaging them by commenting out the following line.
+#mibs:

zabbix-server/tasks/snmp.yml

+---
+- name: ensure snmp software is installed
+  apt: name={{ item }} state=latest
+  with_items:
+    - snmp
+    - snmp-mibs-downloader
+  tags:
+    - snmp
+    - software
+
+- name: ensure the correct snmp.conf is present
+  copy: src=snmp.conf dest=/etc/snmp/snmp.conf
+  tags: 
+    - snmp
+    - config
+
+- name: ensure the snmp MIB libs are present
+  command: download-mibsmibs
+  tags:
+    - snmp
+
+