test(packages_spec): prevent control for `bsd` family

* Refactor `package_name` using `case` like other formulas

test/integration/default/controls/packages_spec.rb

 # Overide by Platform
-package_name = 'openssh-server'
-if platform[:family] == 'suse'
-  package_name = 'openssh'
-end
+package_name =
+  case platform[:family]
+  when 'suse'
+    'openssh'
+  else
+    'openssh-server'
+  end
 
 control 'openssh package' do
   title 'should be installed'
 
+  only_if do
+    platform.family != 'bsd'
+  end
+
   describe package(package_name) do
     it { should be_installed }
   end