libs/utils/env: wipe (by deafult) the results folder
libs/utils/env: wipe (by deafult) the results folder

If a custom results folder is specified, the content of that folder is
wiped out at TestEnv initialization time.

Signed-off-by: Patrick Bellasi <431c86f368affbc3148c4669fbd465131f7e82cb@arm.com>

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