virt: setup TCP chardevice in libvirt driver

Setup the tcp chardevice in the libvirt driver based on the
configuration (if the serial consoles are enabled) and disable the
logging to a file since we have an interactive console.

A new image property is introduced: hw_serial_port_count
A new flavor extra spec is introduced: hw:serial_port_count

Co-Authored-By: Vladan Popovic <vpopovic@redhat.com>
Co-Authored-By: Ian Wells <iawells@cisco.com>
Co-Authored-By: Sushma Korati <sushma_korati@persistent.co.in>

DocImpact
Partial-Implements: blueprint serial-ports
Change-Id: Ic6d24e27d61f600a90ed8fccb525d8b82725903e
Merge "virt: setup TCP chardevice in libvirt driver"