Deprecate support for Arista plugin

... because networking-arista[1] is no longer maintained.

[1] https://opendev.org/x/networking-arista/

Change-Id: Ief13a16ae80deaeacdfa7ca9095a72216972c4f9

manifests/plugins/ml2/arista.pp

@@ -17,6 +17,8 @@
 #
 # == Class: neutron::plugins::ml2::arista
 #
+# DEPRECATED!
+#
 # === Parameters
 #
 # [*eapi_host*]
@@ -55,6 +57,9 @@ class neutron::plugins::ml2::arista(
   include neutron::deps
   require ::neutron::plugins::ml2
 
+  warning('Support for Arista plugin is deprecated and will be removed \
+in a future release')
+
   neutron_plugin_ml2 {
     'ml2_arista/eapi_host'    : value => $eapi_host;
     'ml2_arista/eapi_username': value => $eapi_username;

manifests/plugins/ml2/arista/l3.pp

@@ -17,6 +17,8 @@
 #
 # == Class: neutron::plugins::ml2::arista::l3_arista
 #
+# DEPRECATED!
+#
 # === Parameters
 #
 # [*primary_l3_host*]
@@ -60,6 +62,9 @@ class neutron::plugins::ml2::arista::l3(
   include neutron::deps
   require ::neutron::plugins::ml2
 
+  warning('Support for Arista plugin is deprecated and will be removed \
+in a future release')
+
   if !is_service_default($mlag_config) {
     validate_legacy(Boolean, 'validate_bool', $mlag_config)
     if $mlag_config and is_service_default($secondary_l3_host) {

releasenotes/notes/deprecate-arista-plugin-e3600859c19a9706.yaml

@@ -0,0 +1,5 @@
+---
+deprecations:
+  - |
+    Support for Arista plugin has been deprecated and will be removed in a
+    future release.