Add the api-paste.ini file loader.

When voltracker api server is to be inited, One important step is to
load the api-paste.ini in the etc/ dictionary. So we implement this
file loader in wsgi module.
BTW. most of the code is checked out of nova :-)
Add the wrapper of the wsgi service

Most of the code is copied from glance
Connect the Loader with WSGI service

In glance WSGI server implementation, the loader is explicitly embedded
in api entry file. After I move it in common/wsgi.py as an individual
class, the loader needs to connect to the main wsgi server code.
Add some package requirements

the newly added packeges are need in common/wsgi.py.
Add the voltracker api command line tools

The cmd/api.py is added to parse the command line options, setup the
log, and then boot up the WSGI service.
Also, we add the api entry in setup.cfg to easy installation.
 Update the needed oslo infrastructure modules.