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/pkgs_spec.rb

@@ -0,0 +1,24 @@
+# frozen_string_literal: true
+
+pkgs =
+  case system.platform[:name]
+  when 'arch'
+    %w[salt]
+  when /bsd$/
+    %w[py38-salt]
+  when 'windows'
+    ['Salt Minion']
+  else
+    %w[salt-master salt-minion]
+  end
+
+control 'salt packages' do
+  title 'should be installed'
+
+  pkgs.each do |p|
+    describe package(p) do
+      it { should be_installed }
+      its('version') { should match(/^#{input('saltmajorversion')}/) }
+    end
+  end
+end