Deprecate support for bare SAN driver

The SAN driver is the abstract implementation shared among some volumes
drivers using SAN storage, and can't be actually used in deployments.

We currently maintain options from the base SAN driver in separate
defined resource types for individual drivers, because each driver
uses different set of options.

Change-Id: I33ec1022d9c79fe954f562f4586942efa051bc08

manifests/backend/san.pp

@@ -1,5 +1,6 @@
 # == Class: cinder::backend::san
 #
+# DEPRECATED !!
 # Configures Cinder volume SAN driver.
 # Parameters are particular to each volume driver.
 #
@@ -116,6 +117,8 @@ define cinder::backend::san (
 
   include cinder::deps
 
+  warning('The cinder::backend::san defined resource type is deprecated.')
+
   cinder_config {
     "${name}/volume_backend_name":            value => $volume_backend_name;
     "${name}/backend_availability_zone":      value => $backend_availability_zone;

releasenotes/notes/deprecate-san-f10faba4dedcec43.yaml

@@ -0,0 +1,5 @@
+---
+deprecations:
+  - |
+    The ``cinder::backend::san`` defined resource type has been deprecated and
+    will be removed in a future release.