repmgrd: add %p event notification parameter for "repmgrd_failover_promote"

This enables an event notification script to identify the former primary
node.

doc/appendix-release-notes.xml

@@ -77,7 +77,16 @@
               status.
             </para>
           </listitem>
+
+          <listitem>
+            <para>
+              Add <literal>%p</literal> <link linkend="event-notifications">event notification parameter</link>
+              providing the node ID of the former primary for the <literal>repmgrd_failover_promote</literal> event.
+            </para>
+          </listitem>
+
         </itemizedlist>
+
       </para>
     </sect2>
 

doc/event-notifications.xml

@@ -95,7 +95,8 @@
  </para>
 
  <para>
-   The following parameters are provided for a subset of event notifications:
+   The following parameters are provided for a subset of event notifications; their meaning may
+   change according to context:
  </para>
 
  <variablelist>
@@ -108,6 +109,9 @@
     <para>
      node ID of the demoted primary (<xref linkend="repmgr-standby-switchover"/> only)
     </para>
+    <para>
+     node ID of the former primary (<literal>repmgrd_failover_promote</literal> only)
+    </para>
    </listitem>
   </varlistentry>
   <varlistentry>
@@ -133,7 +137,7 @@
 
  <para>
   The values provided for <literal>%c</literal> and <literal>%a</literal>
-  will probably contain spaces, so should always be quoted.
+  may contain spaces, so should always be quoted.
  </para>
 
  <para>