Fix stable branch releasenotes

This patch fixes stable branch releasenotes by adding respective source
files.

Change-Id: I961933cd15faf000437a434e08de2a10b2875eec
Closes-Bug: #1762962

releasenotes/source/index.rst

@@ -1,8 +1,14 @@
-============================================
+Welcome to Masakari Release Notes documentation!
- masakari Release Notes
+================================================
-============================================
+
+Contents
+========
 
 .. toctree::
    :maxdepth: 1
 
    unreleased
+   queens
+   pike
+   ocata
+

releasenotes/source/ocata.rst

@@ -0,0 +1,7 @@
+===========================
+ Ocata Series Release Notes
+===========================
+
+.. release-notes::
+   :branch: origin/stable/ocata
+

releasenotes/source/pike.rst

@@ -0,0 +1,7 @@
+==========================
+ Pike Series Release Notes
+==========================
+
+.. release-notes::
+   :branch: origin/stable/pike
+

releasenotes/source/queens.rst

@@ -0,0 +1,7 @@
+============================
+ Queens Series Release Notes
+============================
+
+.. release-notes::
+   :branch: origin/stable/queens
+