Fix creation of primitives with PCS

Commit 2cb2f049cbebebeda0b4d10b2325ecb2996fbd99 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 2cb2f049cbebebeda0b4d10b2325ecb2996fbd99 did then break pcs. This
commit fixes that by reverting the changes in pcs.rb.