console: add serial console module

Adds new module console/serial.py to handle configuration
and TCP ports management for the feature serial-ports.

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: new group of option 'serial_console'
Partial-Implements: blueprint serial-ports
Change-Id: Icb7f3569a29a5fab9aaa3a2d441f5fe4e5b55b9f
Merge "console: add serial console module"