Add remove action for plugin

Per #264, add remove action. We still have no way of upgrading.

README.md

@@ -205,7 +205,13 @@ end
 Actions: `:install`, `:remove`
 
 Installs or removes a plugin to a given elasticsearch instance and plugin
-directory.
+directory. Please note that there is currently no way to upgrade an existing
+plugin using commandline tools, so we haven't exposed that feature here either.
+Furthermore, there isn't a way to determine if a plugin is compatible with ES or
+even what version it is. So once we install a plugin to a directory, we
+generally assume that is the desired one and we don't touch it further.
+
+See https://github.com/elastic/cookbook-elasticsearch/issues/264 for more info.
 
 When running a single instance per machine (VM, etc), it's typically
 sufficient to rely on the default value of `plugin_dir`:

libraries/provider_plugin.rb

@@ -28,5 +28,27 @@ class Provider::ElasticsearchPlugin < Chef::Provider::LWRPBase
         end
       end
     end # action
+
+    action :remove do
+      name    = new_resource.plugin_name
+
+      fail 'Could not determine the plugin directory. Please set plugin_dir on this resource.' unless new_resource.plugin_dir
+      converge_by("install plugin #{name}") do
+        plugin_exists = begin
+                          Dir.entries(new_resource.plugin_dir).any? do |plugin|
+                            next if plugin =~ /^\./
+                            name.include? plugin
+                          end
+                        rescue
+                          false
+                        end
+
+        if plugin_exists
+          # automatically raises on error, logs command output
+          shell_out!("#{new_resource.bindir}/plugin -remove #{name}".split(' '), user: new_resource.user, group: new_resource.group)
+          new_resource.updated_by_last_action(true)
+        end
+      end
+    end # action
   end # provider
 end # chef class