cli: update on vm --os-boot does not work as expected(#1012985)

Updating vm --os-bbot does not update the boot order

Fixed by constructing object using factory and set
parameters to it instead of fetching it from server
and updating it.

Change-Id: I34a910a7f1ecae5385e2a6dcd2297a65f419bc9c
Bug-Url: https://bugzilla.redhat.com/1012985
Signed-off-by: Ravi Nori <rnori@redhat.com>