test: centralise all suites into default suite

Modify the `default` suite to use the `saltmajorversion` InSpec input
rather than the `version` variable in `pkgs_spec.rb`.

test/integration/default/controls/service_spec.rb

@@ -0,0 +1,23 @@
+# frozen_string_literal: true
+
+services =
+  case system.platform[:family]
+  when 'bsd'
+    %w[salt_master salt_minion]
+  when 'windows'
+    %w[salt-minion]
+  else
+    %w[salt-master salt-minion]
+  end
+
+control 'salt services' do
+  title 'should be running'
+
+  services.each do |p|
+    describe service(p) do
+      it { should be_installed }
+      it { should be_enabled }
+      it { should be_running }
+    end
+  end
+end