ait-run: Make sure the reports dir exists

Create the directory before trying to store the processed reports
in it.

Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
ait-plot-netperf-udp_stream: The x and y axis captions were reversed

Fix it.

Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>