packaging: less intrusive method for httpd integration

CURRENT IMPLEMENTATION

ovirt-engine proxy all requests, disallow any additional application to
be hosted on the same web server.

NEW IMPLEMENTATION

proxy only ovirt-engine URI prefixes. By default ovirt-engine is at:

  http://host/ovirt-engine

Optionally add redirect from / to /ovirt-engine during setup.

SIDE EFFECTS

In order to handle redirects of 404.html, we require some valid URI to
redirect into, as a result the welcome page of root will not be
index.html but ovirt-engine.html, same for style.css which was renamed
to ovirt-engine-style.css

Change-Id: I89a47a99e28de0905183dc502cb0b35c80f77e6d
Signed-off-by: Alex Lourie <alourie@redhat.com>
Signed-off-by: Alon Bar-Lev <alonbl@redhat.com>