Add tag to package resource

In order to be able to take an action after all the packages of the
module have been installed/updated, we set a 'horizon-package' tag
for each package of this module.

At the moment, there is a generic openstack tag that is not specific
enough if one wants to take action upon a single module change.

Use case :

If an action needs to be taken after all the packages have been
installed or updated : Package <| tag == 'horizon-package' |> -> X

Change-Id: I24ba2ef192536c01c4336d5f15f0ba9564a32b78

manifests/init.pp

@@ -296,7 +296,7 @@ class horizon(
   package { 'horizon':
     ensure => $package_ensure,
     name   => $::horizon::params::package_name,
-    tag    => 'openstack',
+    tag    => ['openstack', 'horizon-package'],
   }
 
   concat { $::horizon::params::config_file:

spec/classes/horizon_init_spec.rb

@@ -28,7 +28,7 @@ describe 'horizon' do
           is_expected.to contain_package('python-lesscpy').with_ensure('present')
           is_expected.to contain_package('horizon').with(
             :ensure => 'present',
-            :tag    => 'openstack'
+            :tag    => ['openstack', 'horizon-package'],
           )
       }
       it { is_expected.to contain_exec('refresh_horizon_django_cache').with({