cmd: update the default behavior of serial console

When using serial console we are expecting using a plain websocket
so we should to return the 'ws://' scheme as the default one, also
it makes no sense to handle webserving content since currently
nothing has been implemented in favor of this case.

DocImpact: The 'base_url' option serial_console has been updated
Closes-Bug: #1373950
Change-Id: I0d0e4f7060febec5e0a357cd3e8c05486f2afaa5
Merge "cmd: update the default behavior of serial console"