Use default install method on Archlinux

Archlinux integration tests were failing because of rabbitmqadmin not being
present. It seems that, while the package exists, it is in the "community"
repo.

Update Python package name to python instead of python2

Partially rolls back voxpupuli#654, though continues to allow the user to set the
package via $rabbitmqadmin_package

data/family/Archlinux.yaml

@@ -1,3 +1,2 @@
 ---
-rabbitmq::python_package: 'python2'
-rabbitmq::rabbitmqadmin_package: 'rabbitmqadmin'
+rabbitmq::python_package: 'python'

spec/classes/rabbitmq_spec.rb

@@ -231,20 +231,15 @@
             end
           end
 
-          if facts[:os]['family'] == 'Archlinux'
-            it 'installs a package called rabbitmqadmin' do
-              is_expected.to contain_package('rabbitmqadmin').with_name('rabbitmqadmin')
-            end
-          else
-            it 'we enable the admin interface by default' do
-              is_expected.to contain_class('rabbitmq::install::rabbitmqadmin')
-              is_expected.to contain_rabbitmq_plugin('rabbitmq_management').with(
-                notify: 'Class[Rabbitmq::Service]'
-              )
-              is_expected.to contain_archive('rabbitmqadmin').with_source('http://1.1.1.1:15672/cli/rabbitmqadmin')
-            end
+          it 'we enable the admin interface by default' do
+            is_expected.to contain_class('rabbitmq::install::rabbitmqadmin')
+            is_expected.to contain_rabbitmq_plugin('rabbitmq_management').with(
+              notify: 'Class[Rabbitmq::Service]'
+            )
+            is_expected.to contain_archive('rabbitmqadmin').with_source('http://1.1.1.1:15672/cli/rabbitmqadmin')
           end
-          it { is_expected.to contain_package('python') } if %w[RedHat Debian SUSE].include?(facts[:os]['family'])
+
+          it { is_expected.to contain_package('python') } if %w[RedHat Debian SUSE Archlinux].include?(facts[:os]['family'])
           it { is_expected.to contain_package('python2') } if %w[FreeBSD OpenBSD].include?(facts[:os]['family'])
         end