movistar_u7d.py: add back minimal timeit probes and log the precise

switching times, both for live channels (in the millisecond range)
and vod programs (from 300 and something milliseconds all the way
up to 700-800 even, depending on Movistar's servers's response times)

Signed-off-by: Javier Marcet <javier@marcet.info>