[datadog_monitor] Fix crash for jmx integrations with init_config att…

…ributes set (#869)

Fixes a crash when the init_config attribute for a jmx integration (such asignite, jboss_wildfly) is set.

Previously, the init_config attribute would be merged in-place (through the merge! method) with another hash: { 'is_jmx': true, 'collect_default_metrics': true }. This would cause a crash if init_config is defined in attributes, because chef attributes cannot be modified that way:

================================================================================
Error executing action `add` on resource 'datadog_monitor[jboss_wildfly]'
================================================================================

Chef::Exceptions::ImmutableAttributeModification
------------------------------------------------
Node attributes are read-only when you do not specify which precedence level to set. To set an attribute use code like `node.default["key"] = "value"'

Cookbook Trace: (most recent call first)
----------------------------------------
/tmp/kitchen/cache/cookbooks/datadog/resources/monitor.rb:67:in `block (2 levels) in class_from_file'
/tmp/kitchen/cache/cookbooks/datadog/resources/monitor.rb:43:in `block in class_from_file'

This PR fixes this by not merging the attributes in-place. It also adds a kitchen test which exhibits the previous faulty behavior.

kitchen.yml

@@ -595,3 +595,16 @@ suites:
         instances:
           - host: localhost
             port: 49112
+
+- name: datadog_jboss_wildfly
+  run_list:
+    - recipe[datadog::jboss_wildfly]
+  attributes:
+    datadog:
+      <<: *DATADOG
+      jboss_wildfly:
+        init_config:
+          custom_jar_paths: ["/opt/wildfly/bin/client/jboss-client.jar"]
+        instances:
+          - jmx_url: localhost:9990
+            tools_jar_path: /opt/wildfly/bin/client/jboss-client.jar

resources/monitor.rb

@@ -78,7 +78,7 @@
     init_config = new_resource.init_config
     if new_resource.is_jmx
       init_config ||= {}
-      init_config.merge!({ 'is_jmx': true, 'collect_default_metrics': true })
+      init_config = init_config.merge({ 'is_jmx': true, 'collect_default_metrics': true })
     end
 
     variables(