Accept a string as extraInitContainers value for filebeat

This makes the filebeat chart consistent with the other beats, while
preserving backwards compatibility.

Fixes #490

filebeat/templates/daemonset.yaml

@@ -87,7 +87,17 @@ spec:
       {{- end }}
       {{- if .Values.extraInitContainers }}
       initContainers:
+      # All the other beats accept a string here while
+      # filebeat accepts a valid yaml array. We're keeping
+      # this as a backwards compatible change, while adding
+      # also a way to pass a string as other templates to
+      # make these implementations consistent.
+      # https://github.com/elastic/helm-charts/issues/490
+      {{- if eq "string" (printf "%T" .Values.extraInitContainers) }}
+{{ tpl .Values.extraInitContainers . | indent 8 }}
+      {{- else }}
 {{ toYaml .Values.extraInitContainers | indent 8 }}
+      {{- end }}
       {{- end }}
       containers:
       - name: "filebeat"

filebeat/tests/filebeat_test.py

@@ -74,7 +74,7 @@ def test_adding_a_extra_container():
     } in extraContainer
 
 
-def test_adding_init_containers():
+def test_adding_init_containers_as_yaml():
     config = """
 extraInitContainers:
 - name: dummy-init
@@ -90,6 +90,22 @@ def test_adding_init_containers():
     } in initContainers
 
 
+def test_adding_init_containers():
+    config = """
+extraInitContainers: |
+  - name: dummy-init
+    image: busybox
+    command: ['echo', 'hey']
+"""
+    r = helm_template(config)
+    initContainers = r["daemonset"][name]["spec"]["template"]["spec"]["initContainers"]
+    assert {
+        "name": "dummy-init",
+        "image": "busybox",
+        "command": ["echo", "hey"],
+    } in initContainers
+
+
 def test_adding_image_pull_secrets():
     config = """
 imagePullSecrets: