Add new command line option for rn_ls utility to sort result by
various fields:
-r parameters sort output by several columns; the parameters may contain the following
items (where first symbol is for ascending and second for descending order):
n | N - sort by run number;
m | M - sort by database name;
d | D - sort by duration;
p | P - sort by partition names;
u | U - sort by user names;
h | H - sort by hostnames;