test(service_spec): add `should be_installed`

test/integration/v201803-py2/controls/service_spec.rb

@@ -8,6 +8,7 @@ control 'salt services' do
     salt-minion
   ].each do |p|
     describe service(p) do
+      it { should be_installed }
       it { should be_enabled }
       it { should be_running }
     end

test/integration/v201902-py2/controls/service_spec.rb

@@ -8,6 +8,7 @@ control 'salt services' do
     salt-minion
   ].each do |p|
     describe service(p) do
+      it { should be_installed }
       it { should be_enabled }
       it { should be_running }
     end

test/integration/v201902-py3/controls/service_spec.rb

@@ -8,6 +8,7 @@ control 'salt services' do
     salt-minion
   ].each do |p|
     describe service(p) do
+      it { should be_installed }
       it { should be_enabled }
       it { should be_running }
     end

test/integration/v3000-py3/controls/service_spec.rb

@@ -8,6 +8,7 @@ control 'salt services' do
     salt-minion
   ].each do |p|
     describe service(p) do
+      it { should be_installed }
       it { should be_enabled }
       it { should be_running }
     end