Make rabbitmq_plugin resource functional on RabbitMQ 3.10.x

The rabbitmq_plugin resource use the "rabbitmq-plugins"-command when
enumerating enabled plugins.  Starting with rabbitmq 3.10, this command
will output a informational message:
'Listing plugins with pattern ".*" ...' which can be hidden with the -s
or -q parameter.  However, this approach will break rabbitmq_plugin on
older versions of RabbitMQ.

This patch implements a workaround that simply ignores the outputted line
if it exists.

Fixes: voxpupuli#909

Author: kvisle

lib/puppet/provider/rabbitmq_plugin/rabbitmqplugins.rb

@@ -12,6 +12,7 @@ def self.instances
     end
 
     plugin_list.split(%r{\n}).map do |line|
+      next if line.start_with?('Listing plugins')
       raise Puppet::Error, "Cannot parse invalid plugins line: #{line}" unless line =~ %r{^(\S+)$}
 
       new(name: Regexp.last_match(1))

spec/unit/puppet/provider/rabbitmq_plugin/rabbitmqctl_spec.rb

@@ -22,6 +22,16 @@
     provider.create
   end
 
+  context 'with RabbitMQ version >=3.10.0' do
+    it 'matches plugins' do
+      provider.expects(:rabbitmqplugins).with('list', '-E', '-m').returns <<~EOT
+        Listing plugins with pattern ".*" ...
+        foo
+      EOT
+      expect(provider.exists?).to eq(true)
+    end
+  end
+
   context 'with RabbitMQ version >=3.4.0' do
     it 'calls rabbitmqplugins to enable' do
       provider.class.expects(:rabbitmq_version).returns '3.4.0'