Error on API Guide warnings

Error on warnings in building the API guide and fix any problem
encountered:
* tox.ini: Enable tread warnings as errors
* index.rst: Add unreferenced file extra_specs_and_properties as
  hidden file so that it does not show up in index. It is still
  built and will be referenced from other files.
* general_info.rst: Remove reference to non-existing file
* server_concept: Add missing empty line after code directives

Also fix a typo and remove extra EOL whitespace.

Change-Id: Ie766f8d2f7d82b7b5b02541b342f9829ca4550a0

api-guide/source/general_info.rst

@@ -249,7 +249,8 @@ on compute hosts rather than servers.
 
 -  **Aggregates**
 
-   Please see :doc:`aggregates.rst`
+   See `Aggregates developer information
+   <http://docs.openstack.org/developer/nova/aggregates.html>`_.
 
 -  **Migrations**
 

api-guide/source/index.rst

@@ -87,3 +87,8 @@ Contents
     paginated_collections
     polling_changes-since_parameter
     request_and_response_formats
+
+.. toctree::
+    :hidden:
+
+    extra_specs_and_properties

api-guide/source/server_concepts.rst

@@ -150,6 +150,7 @@ be used and interpreted by nova.
    and pagination.
 
 .. code::
+
    Precondition:
    there are 2 servers existing in cloud with following info:
 
@@ -168,6 +169,7 @@ be used and interpreted by nova.
    **Example: General user query server with administrator only options**
 
 .. code::
+
    Request with non-administrator context:
    GET /servers/detail?locked=1
    Note that 'locked' is not returned through API layer
@@ -189,6 +191,7 @@ be used and interpreted by nova.
    **Example: Administrator query server with administrator only options**
 
 .. code::
+
    Request with administrator context:
    GET /servers/detail?locked=1
 
@@ -213,6 +216,7 @@ be used and interpreted by nova.
    **Example: User query server using exact matching on host**
 
 .. code::
+
    Precondition:
    Request with administrator context:
    GET /servers/detail
@@ -248,10 +252,11 @@ be used and interpreted by nova.
        }
        ]
    }
-   
+
    **Example: Query server using regex matching on name**
 
 .. code::
+
    Precondition:
    Request with administrator context:
    GET /servers/detail
@@ -305,6 +310,7 @@ be used and interpreted by nova.
    regex matching on name**
 
 .. code::
+
    Precondition:
    Request with administrator context:
    GET /servers/detail
@@ -346,7 +352,7 @@ be used and interpreted by nova.
        ]
    }
 
--  **Speical keys are used to tweek the query**
+-  **Special keys are used to tweek the query**
    ``changes-since`` returns instances updated after the given time,
    ``deleted`` return (or exclude) deleted instances and ``soft_deleted``
    modify behavior of 'deleted' to either include or exclude instances whose
@@ -355,6 +361,7 @@ be used and interpreted by nova.
    **Example: User query server with special keys changes-since**
 
 .. code::
+
    Precondition:
    GET /servers/detail
 
@@ -371,7 +378,7 @@ be used and interpreted by nova.
            "updated": "2015-12-17T15:55:52Z"
            ...
        }
-   }    
+   }
 
    GET /servers/detail?changes-since='2015-12-16T15:55:52Z'