virt-libvirt: Setup libvirt serial_console in start()

Before it was only ever setup during create().  As soon as
a vm object was started from scratch, it never got created.
Also removed libvirt_vm.VM.only_pty to always use virsh console
which should be more reliable and still support all types.  Added
a fixme in create() -> add_serial() to investigate older libvirt
additional serial addition at install.

Signed-off-by: Chris Evich <cevich@redhat.com>
virt: Timeout Cleanup

* Made post-process use the vm instance LOGIN_WAIT_TIMEOUT attribute
* Removed redefinition of inherited qemu_vm.VM attributes, update comment.

Signed-off-by: Chris Evich <cevich@redhat.com>
virt-libvirt: Add simple kernel-panic test

Simple validation for vm.verify_kernel_crash()

Signed-off-by: Chris Evich <cevich@redhat.com>