packaging: introduce generic file serving

current implementation adds a reference for each file within root
web.xml, this is inflexible to manage and add new files as needed.

new implementation defines maps /ovirt-engine-files URI into
/usr/share/ovirt-engine/files, every file within that directory will be
exposed to application.

packaging can add misc files or symlinks to expose files based on
specific location or capabilities.

moved:
1. spice
2. spice-html5
3. novnc

usbfilter.txt moved out of spice directory as it is application provided
and not spice artifact.

Change-Id: I1cd8b39ff2647bc006e09d50c9fc7088fcef7434
Signed-off-by: Alon Bar-Lev <alonbl@redhat.com>