Enable no_parent and file_only security

The websockify package was recently upgraded to version 0.5.1, which added two
parameters that provide additional security:
* no_parent - returns 403 response if contents out of the web root are
requested. Required to disable directory traversal.
* file_only - returns 404 response if non-file contents are requested. Required
to disable directory listing.
This version is available in PyPi.

Nova should upgrade it's required version for websockify, and set these
parameters while creating and starting the NovaWebSocketProxy to ensure
better security.

DocImpact
Fixes bug #1195700

Change-Id: I9c4b28eb1b384048f10d365ed204b916afd371bb
Merge "Enable no_parent and file_only security"