Add samples to serve API through Apache mod_wsgi

The default API service (ironic.cmd.api) uses the wsgiref library.

Some deployers may want to serve the API through apache/httpd instead.

This patch adds application hooks to use with mod_wsgi, and a sample
apache2 config file to demonstrate its use with debian-based distros.

Change-Id: I44cd8e0941c350a6e5c16cf2d068c3e8d684ab47
Related-bug: #1279206
Merge "Add samples to serve API through Apache mod_wsgi"