CSIT: Do not autogenerate csv persistance plot file names.

CSIT: Do not autogenerate csv persistance plot file names.

History of plotss is lost when JJB generates new file names
on every commit to ci-management.

plot:
 csv-file-name (str) – Use for choosing the file name in which the
 data will be persisted. If none specified and random name is
 generated as done in the Jenkins Plot plugin. (default: random
 generated .csv filename, same behaviour as the Jenkins Plot plugin)

Change-Id: I1fe55eb035c168f489437f4617c41f877b9a9bc1
Signed-off-by: Miroslav Miklus <mmiklus@cisco.com>