Fix doctest for utils.find_nearest_host()

The method check for port 22 which thus assume the host running the
doctest has something listening (usually ssh) on that port.  That is not
always the case.

Instead create a listening socket on localhost and invoke
find_nearest_host() on that port.

Drawback: that makes the example non obvious :-/

Change-Id: Id328954daeac0685a10b0aac9358cf0b853180a6
Merge "Fix doctest for utils.find_nearest_host()"