webadmin: Warning message for cloning a VM with LUN.

When cloning a VM with an attached LUN, a warning message added
which informs the user that the LUN won't be cloned as well. the
user should know this when cloning a VM.

Change-Id: Icb2d5205baaadd17646b5076bf5f3add481f0709
Bug-Url: https://bugzilla.redhat.com/1152023
Signed-off-by: Amit Aviram <aaviram@redhat.com>