instead of printing it out after samplings, we should print it
in between them. as toppartitions_test.py in dtest splits the
samplings using "\n\n". without this change, dtest would consider
the empty line as another sampling and then fail the test. as
the empty sampling does not match with the expected regular expressions.
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>