Fix docstrings for sphinx

Sphinx complains about:
docstring of nova.conf.opts:5: ERROR: Unexpected indentation.
docstring of nova.conf.opts:8: WARNING: Block quote ends without a blank line; unexpected unindent.
doc/source/threading.rst:34: WARNING: Literal block ends without a blank line; unexpected unindent.

Fix these problems.

Change-Id: I023487445b21891e9488a5f6eef9f89f9cecade0

doc/source/threading.rst

@@ -31,6 +31,7 @@ delays in the case that there is only a single green thread::
 	from eventlet import greenthread
 	...
 	greenthread.sleep(0)
+
 In current code, time.sleep(0）does the same thing as greenthread.sleep(0) if
 time module is patched through eventlet.monkey_patch(). To be explicit, we recommend
 contributors use ``greenthread.sleep()`` instead of ``time.sleep()``.

nova/conf/opts.py

@@ -17,10 +17,11 @@
 This is the single point of entry to generate the sample configuration
 file for Nova. It collects all the necessary info from the other modules
 in this package. It is assumed that:
+
 * every other module in this package has a 'list_opts' function which
   return a dict where
-   * the keys are strings which are the group names
-   * the value of each key is a list of config options for that group
+  * the keys are strings which are the group names
+  * the value of each key is a list of config options for that group
 * the nova.conf package doesn't have further packages with config options
 * this module is only used in the context of sample file generation
 """