repmgr: have "cluster show" exit with a non-zero value if issues detected

If any issues are detected (e.g. node not reachable, unexpected node status
etc.), "repmgr cluster show" returns exit code 25 ("ERR_NODE_STATUS").

Note that exit code 25 was introduced recently as "ERR_CLUSTER_CHECK",
however it makes sense to use this to indicate issues detected by any
command which can detect node issues.

Addresses GitHub #456.

doc/appendix-release-notes.sgml

@@ -46,6 +46,12 @@
             </para>
           </listitem>
 
+          <listitem>
+            <para>
+              <command><link linkend="repmgr-cluster-show">repmgr cluster-show</link></command>
+              returns non-zero exit code if node status issues detected (GitHub #456).
+            </para>
+          </listitem>
 
           <listitem>
             <para>
@@ -76,7 +82,7 @@
 
           <listitem>
             <para>
-              <application>repmgr</application>: fix <command><link linkend="repmgr-standby-register">repmgr standby register--wait-sync </link></command>
+              <application>repmgr</application>: fix <command><link linkend="repmgr-standby-register">repmgr standby register --wait-sync</link></command>
               when no timeout provided.
             </para>
           </listitem>

doc/repmgr-cluster-crosscheck.sgml

@@ -56,7 +56,7 @@
       </varlistentry>
 
       <varlistentry>
-        <term><option>ERR_CLUSTER_CHECK (25)</option></term>
+        <term><option>ERR_NODE_STATUS (25)</option></term>
         <listitem>
           <para>
             One or more nodes could not be reached.

doc/repmgr-cluster-matrix.sgml

@@ -116,7 +116,7 @@
       </varlistentry>
 
       <varlistentry>
-        <term><option>ERR_CLUSTER_CHECK (25)</option></term>
+        <term><option>ERR_NODE_STATUS (25)</option></term>
         <listitem>
           <para>
             One or more nodes could not be reached.

doc/repmgr-cluster-show.sgml

@@ -113,4 +113,33 @@
     </para>
   </refsect1>
 
+
+  <refsect1>
+    <title>Exit codes</title>
+    <para>
+      Following exit codes can be emitted by <command>repmgr cluster show</command>:
+    </para>
+    <variablelist>
+
+      <varlistentry>
+        <term><option>SUCCESS (0)</option></term>
+        <listitem>
+          <para>
+            No issues were detected.
+          </para>
+        </listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><option>ERR_NODE_STATUS (25)</option></term>
+        <listitem>
+          <para>
+            One or more issues were detected.
+          </para>
+        </listitem>
+      </varlistentry>
+
+   </variablelist>
+  </refsect1>
+
 </refentry>