Add servers_per_port parameter in object-server

According to the doc at this URL:
https://docs.openstack.org/swift/latest/deployment_guide.html

for performance reasons, it is desirable to use forks of the
object-server, each on a different port, one per device. This
is what I'm doing in openstack-cluster-install in Debian. For
this, I've been using this patch. It'd be nice to have it
upstream as well.

Change-Id: I9224eb7022871e92cc18f82e9985d91d5e0c2823

manifests/storage/server.pp

@@ -47,6 +47,14 @@
 #   writing to the root device.
 #   Defaults to true.
 #
+# [*servers_per_port*]
+#   (optional) Spawn multiple servers per device on different ports.
+#   Make object-server run this many worker processes per unique port of
+#   "local" ring devices across all storage policies.  This can help provide
+#   the isolation of threads_per_disk without the severe overhead.  The default
+#   value of 0 disables this feature.
+#   Defaults to 0.
+#
 # [*user*]
 #   (optional) User to run as
 #   Defaults to 'swift'.
@@ -151,6 +159,7 @@ define swift::storage::server(
   $max_connections                = 25,
   $pipeline                       = ["${type}-server"],
   $mount_check                    = true,
+  $servers_per_port               = 0,
   $user                           = 'swift',
   $workers                        = $::os_workers,
   $allow_versions                 = false,

templates/object-server.conf.erb

@@ -3,6 +3,7 @@ devices = <%= @devices %>
 bind_ip = <%= @storage_local_net_ip %>
 bind_port = <%= @bind_port %>
 mount_check = <%= @mount_check %>
+servers_per_port = <%= @servers_per_port %>
 user = <%= @user %>
 log_name = <%= @log_name %>
 log_facility = <%= @log_facility %>