analysis/tasks: reformat capacity thresholds
analysis/tasks: reformat capacity thresholds

When multiple signals are plotted there is a good chance that the line
style currently used for cluster capacity thresholds makes the plots hard
to parse.

This change style and colors to make these thresholds less intrusive.

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

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