tests/eas/capacity-capping: Don't let target latency influence phase times
tests/eas/capacity-capping: Don't let target latency influence phase times

This test assumes that the artificial constraints transitioned at specific
times, and uses  `time.sleep` to space out these transitions. However in between
these `time.sleep` calls it writes values on the target, which can take
significant time.

Measure the latency of this write, then subtract that latency from the time to
sleep.

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