Update the openstack common modules.

Add some new modules which are defined in openstack-common.conf.
Add the WSGI router for Voltracker v1 API

this router is used for http server to router the request to specifical
applications by url address. At current time, we only add the maps of
volume operations.
A simple and native implementation of binary tree

To track the topology of nova-compute node which has the specific
volume, we must use some graph(or tree) data structure to make it
easier. At the current version, we choose binary tree structure.

* new node can be added in tree or node can be removed arbitrarily, but
  each node must have at most two children and exactly one parent(except
  the root).
* the node remove function need to be optimized to keep the tree more
  balanced.
Add the api-paste loader and cert validate tool.

* api-paste Loader can automate search the api-paste.ini file and load
  the specific application.
* cert validate utility is used when ssl is enabled when start the api
  wsgi app
Add the voltracker domian sepcific policy enforcer

Most of the code is port from glance.
Copy some useful tools from oslo-incubator
Add the api-paste.ini file to define the WSGI apps

To make performance test easier, we now use the unauth-context to avoid
the keystone authorization.
Update the required packeges list.
Update the required openstack common modules list
Add utils to track the version information

Openstack provide pbr to make version management easier. To get the
version string of package, what we need to do is only calling the
related function.
Remove the pbr version requirements in setup.py
Update the required packeges list for unit tests
Move the explicit paste app load out of api.py
Add some openstack common modules

The follow library modules are added to voltracker:
* context.py: store information about the security context under which
  the user accesses the system, as well as additional request info.
* exception.py: voltracker exception subclasses.
* service.py: add function to perpare the service context.
Add __init__.py to voltracker/executor subpackage
Merge branch 'add_api'