Add Plot plugin support

This publisher provides generic plotting (or graphing) capabilities in
Jenkins with Plot plugin.

Implements: blueprint jenkins-job-builder-plot
Change-Id: I7a957357fb25c2537f9b62a5354ea796268fe5c6
Signed-off-by: Emilien Macchi <emilien.macchi@enovance.com>

Conflicts:
	jenkins_jobs/modules/publishers.py
	setup.py
Fix plot plugin support

In case of using CSV or XML source file for plotting, the xml block
now includes the file to be plotted. Docs updated to match current
behaviour.

Change-Id: If613ebf08948d289be2c9be7dcdd8b7973f745f1
Closes-Bug: #1221326
Fix plot plugin support

Based on the source code of the jenkins plot plugin
https://github.com/jenkinsci/plot-plugin/ the related publisher
has been updated to generate a working XML block and match the
behaviour for data persistency in CSV file with random generated
name.
Minor code adjustement to match coding covention (Hyphen and
capital letter usage)
Plot group now correctly handled.
All three type of plot with different option are covered in tests.

Change-Id: I6bd22ea19f397cf2123b924ff5517682a53177ed
Closes-Bug: #1223017

Conflicts:
	jenkins_jobs/modules/publishers.py