[kibana] Add subPath support to secretMounts

Fixes: #229

This is needed in situation where you need to mount a specific secret as
a file in a directory that contains other files. This was added for the
Elasticsearch chart to make it possible to mount the keystore, the same
option is needed for Kibana too as seen in in #229.

kibana/templates/deployment.yaml

@@ -109,6 +109,9 @@ spec:
           {{- range .Values.secretMounts }}
           - name: {{ .name }}
             mountPath: {{ .path }}
+            {{- if .subPath }}
+            subPath: {{ .subPath }}
+            {{- end }}
           {{- end }}
           {{- range $path, $config := .Values.kibanaConfig }}
           - name: kibanaconfig

kibana/tests/kibana_test.py

@@ -355,4 +355,34 @@ def test_override_imagePullPolicy():
 
     r = helm_template(config)
     c = r['deployment'][name]['spec']['template']['spec']['containers'][0]
-    assert c['imagePullPolicy'] == 'Always'
+    assert c['imagePullPolicy'] == 'Always'
+
+def test_adding_a_secret_mount_with_subpath():
+    config = '''
+secretMounts:
+  - name: elastic-certificates
+    secretName: elastic-certs
+    path: /usr/share/elasticsearch/config/certs
+    subPath: cert.crt
+'''
+    r = helm_template(config)
+    d = r['deployment'][name]['spec']['template']['spec']
+    assert d['containers'][0]['volumeMounts'][-1] == {
+        'mountPath': '/usr/share/elasticsearch/config/certs',
+        'subPath': 'cert.crt',
+        'name': 'elastic-certificates'
+    }
+
+def test_adding_a_secret_mount_without_subpath():
+    config = '''
+secretMounts:
+  - name: elastic-certificates
+    secretName: elastic-certs
+    path: /usr/share/elasticsearch/config/certs
+'''
+    r = helm_template(config)
+    d = r['deployment'][name]['spec']['template']['spec']
+    assert d['containers'][0]['volumeMounts'][-1] == {
+        'mountPath': '/usr/share/elasticsearch/config/certs',
+        'name': 'elastic-certificates'
+    }