Do not override disk_cache settings for RBD disks
Do not override disk_cache settings for RBD disks

Currently disk_cache settings other than none will be overridden to
none. RBD is considered safe and well behaved when it comes to
live migration and other cache sensitive issues.

Fixes #822.

Signed-off-by: Oleander Reis <c1e5e96160e3c099f76a8b863f1467b1162cc44c@hostserver.de>

ganeti/ganeti,ganeti/ganeti,ganeti/ganeti