KVM: fix RebootInstance
KVM: fix RebootInstance

RebootInstance was broken, because it just used to call StartInstance
with wrong parameters. With this patch we still stop the instance, but
use the saved kvm runtime to start it again.

Reviewed-by: iustinp


apyrgio/snf-ganeti,ganeti/ganeti,andir/ganeti,apyrgio/ganeti,andir/ganeti,yiannist/ganeti,bitemyapp/ganeti,bitemyapp/ganeti,apyrgio/snf-ganeti,leshchevds/ganeti,dimara/ganeti,yiannist/ganeti,dimara/ganeti,mbakke/ganeti,onponomarev/ganeti,ganeti-github-testing/ganeti-test-1,apyrgio/ganeti,onponomarev/ganeti,andir/ganeti,mbakke/ganeti,ganeti/ganeti,ganeti/ganeti,leshchevds/ganeti,grnet/snf-ganeti,leshchevds/ganeti,mbakke/ganeti,ganeti-github-testing/ganeti-test-1,grnet/snf-ganeti,yiannist/ganeti