pve-sheepdog : bump to 0.8.0

Please note that sheepdog 0.8 cluster format is not compatible with < 0.8 sheepdog format.

you need to backup your vdi before upgrade, and restore them after.

They are no upgrade path

Signed-off-by: Alexandre Derumier <aderumier@odiso.com>
add sources for 0.8.0