start host vm: now define the domain and then start

before we were doing transient domain, this patch implement
persisten domain.

This will allow us to do restart of domain after physical
container is restarted
stop host vm: undefine the domain when stopping it
remove host vm: undefine the domain if necessary

if the user has powered off VM machine the domain might still be
defined
start host vm: make VM start at boot if kvm_autostart attr is defined

When kvm_autostart attribute is defined the VM will be automatically
started at boot time when the physical container boot (this is done
by libvirt)
start host vm: document the kvm_autostart
kvm commands: minor code refactoring

Created a getPhysNode function in vmextended.py and remove all the
duplicated code in all over the place.

Results: 8 files changed, 58 insertions(+), 114 deletions(-)

56 lines of code removed!!