Adds os-volumes_attachments info to Compute v 2.1

Change-Id: Ifb95bc969742e23ab5b2b8c7f2ba6185e13e6668
Closes-bug: 1539255

api-ref/src/docbkx/ch_compute-v2.1.xml

@@ -364,7 +364,7 @@
       href="../wadls/compute-api/src/v2.1/wadl/os-virtual-interfaces-v2.1.wadl"
       xmlns:wadl="http://wadl.dev.java.net/2009/02"/>
   </section>
-  <!-- <section xml:id="os-volume-attachments-v2.1">
+  <section xml:id="os-volume-attachments-v2.1">
     <title>Servers with volume attachments (servers, os-volume_attachments)</title>
     <para>
       Attaches volumes that are created through the volume API to server
@@ -374,7 +374,7 @@
     <wadl:resources
       href="../wadls/compute-api/src/v2.1/wadl/os-volume-attachments-v2.1.wadl"
       xmlns:wadl="http://wadl.dev.java.net/2009/02"/>
-  </section> -->
+  </section>
   <section xml:id="os-flavors-v2.1">
     <title>Flavors with extended attributes (flavors)</title>
     <para>