ipynb: fix LISA_HOME identification if realpath is not available
ipynb: fix LISA_HOME identification if realpath is not available

This patch makes the identification of the LISA installation folder
more robust by depending only on standard shell commands.

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

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