telegraf-extra-plugin.conf.j2: fix template typo

Related to commend : 3cccb6ba50 (r31366694)

Fix typo added in template `telegraf-extra-plugin.conf.j2`

Also add molecule tests to validate file generated with `telegraf_plugins_extra` option.

The added test template come from `Multiple inputs of the same type` (https://github.com/influxdata/telegraf/blob/master/docs/CONFIGURATION.md#multiple-inputs-of-the-same-type)

molecule/default/molecule.yml

@@ -28,6 +28,15 @@ provisioner:
   inventory:
     group_vars:
       all:
+        telegraf_plugins_extra:
+          percpu-usage:
+            plugin: cpu
+            config:
+              - percpu = true
+              - totalcpu = false
+              - name_override = "percpu_usage"
+              - fielddrop = ["cpu_time*"]
+
         telegraf_plugins_default:
           - plugin: cpu
             config:

molecule/default/tests/test_default.py

@@ -21,6 +21,15 @@ def test_telegraf_dot_conf(File):
     assert telegraf.contains('[[inputs.cpu]]')
 
 
+def test_telegraf_dot_d(File):
+    telegraf = File("/etc/telegraf/telegraf.d/percpu-usage.conf")
+    assert telegraf.user == "telegraf"
+    assert telegraf.group == "telegraf"
+    assert telegraf.mode == 0o640
+    assert telegraf.contains('[[inputs.cpu]]')
+    assert telegraf.contains('totalcpu = false')
+
+
 def test_telegraf_package(Package, SystemInfo):
     telegraf = Package('telegraf')
     assert telegraf.is_installed