Re-add keystone-manage credential_setup

The step that ran keystone-manage credential_setup has been removed
as "deprecated" with the "Initial identity Pike updates" [1].

However, the Pike CLI documentation for keystone-manage does not
indicate that the command is deprecated [2] and the install-guide
continues to use it [3].

Also, I got this error message on a Pike installation (Ubuntu):

ERROR keystone.common.fernet_utils [...] Either [credential] key_repository
does not exist or Keystone does not have sufficient permission to access
it: /etc/keystone/credential-keys/

For these reasons, this patch reinstates the keystone-manage
credential_setup step.

[1] commit 5279aa4fbc
    (Change-Id: I518ed83f7e19c590e7846160889faf46db274b3a)
[2] https://docs.openstack.org/keystone/pike/cli/index.html
[3] https://docs.openstack.org/keystone/pike/install/keystone-install-ubuntu.html

Change-Id: Iad5afd70ab99d968a6546bd19e5e5831a8299a49

recipes/server-apache.rb

@@ -131,6 +131,16 @@ execute 'fernet setup' do
       --keystone-user #{keystone_user}
       --keystone-group #{keystone_group}
   EOH
+  notifies :run, 'execute[credential setup]', :immediately
+end
+
+execute 'credential setup' do
+  user 'root'
+  command <<-EOH.gsub(/\s+/, ' ').strip!
+        keystone-manage credential_setup
+      --keystone-user #{keystone_user}
+      --keystone-group #{keystone_group}
+  EOH
 end
 
 # define the address to bind the keystone apache main service to