Initial upstart support

Basic hvc0 upstart file
Basic xvc0 upstart file

This file is required for get console on modern OS with old xvc0 console (dom0 RHEL5)
At RHEL6 / CentOS6 domU should have 2.6.32 kernel

CentOS5 init process has a problem with communication between newest kernel and console (console stop responds when switched into init 3)
Better way to handle /dev/hvc0
Refactoring of pygrub discovery && default console

Some cleanups for pygrub discovery process. For now for Xen domU on a RHEL6
the default console is hvc0 (kernels > 2.6.22 uses hvc0)
For RHEL5 it is xvc0 (kernel == 2.6.18)