Fix creation of primitives with PCS

Commit 755f3c9ea279fc6ebba4e4fc66165528a45b367f breaks pcs support to
create primitives. This is because the "crm" way to update the cluster
is by flattening an array where for pcs we call the command with
arguments as an array.

Commit 755f3c9ea279fc6ebba4e4fc66165528a45b367f did then break pcs. This
commit fixes that by reverting the changes in pcs.rb.