core, engine, userportal, webadmin: Fix balloon device presence in VM pools

During the creation of VM pools the balloon device was enabled
regardless if the user disabled it in the VM Pool Dialog. This
patch fixes this bug.

Change-Id: I379532f2a62ff16d8d11f34d62896125569197a1
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1150777
Signed-off-by: Vitor de Lima <vdelima@redhat.com>