Add interval_slow parameter to mysql input plugin

Change-Id: I5d1df2290fc5a2018978e8b5743cf361c51f5876
diff --git a/telegraf/files/input/mysql.conf b/telegraf/files/input/mysql.conf
index 3566535..3d32300 100644
--- a/telegraf/files/input/mysql.conf
+++ b/telegraf/files/input/mysql.conf
@@ -1,5 +1,6 @@
 {%- if values.address is defined %}
 [[inputs.mysql]]
   servers = [ "{{ values.username }}:{{ values.password }}@{{ values.protocol|default("unix") }}({{ values.address }})/" ]
+  interval_slow = "{{ values.interval_slow|default("15m") }}"
 {%- include 'telegraf/files/input/_tags.conf' %}
 {%- endif %}