LisaTest: Add get_trace method
LisaTest: Add get_trace method

It's a good idea to unify the creation of Traces in one place, because
passing a different sent of events will result in different time
indexes due to the time normalization being based on the time of the
first event.

This is also a nice convenience method.

mdigiorgio/lisa,credp/lisa,joelagnel/lisa,ARM-software/lisa,ARM-software/lisa,credp/lisa,bjackman/lisa,credp/lisa,mdigiorgio/lisa,joelagnel/lisa,bjackman/lisa,ARM-software/lisa,arnoldlu/lisa,ARM-software/lisa,arnoldlu/lisa,credp/lisa