utils/analysis: Fix overutilized plotting
Created by: valschneider
The last event's duration will always be set to NaN, because the time delta is computed as (next_event time - cur_event time). Since the plotOverutilized() method uses the time deltas to render the overutilized flag, this can break things: if the last status event reports overutilized=1, it won't be rendered (see https://github.com/ARM-software/lisa/issues/433).
This fixes that by 'manually' setting the duration of the last event.