Add parameters to plotting scripts

Add `imgname` parameter to be able to save a plot to a file instead of
showing it. Use-case: platforms without GUI like docker containers.

Add `labels` parameter to histogram plot. Use-case: replacing long
commands with human friendly labels.

scripts/plot_parametrized.py

@@ -25,6 +25,7 @@ parser.add_argument(
 parser.add_argument(
     "--titles", help="Comma-separated list of titles for the plot legend"
 )
+parser.add_argument("--imgname", help="Save image to the given filename.")
 
 args = parser.parse_args()
 if args.parameter_name is not None:
@@ -100,4 +101,7 @@ if args.log_x:
 if args.titles:
     plt.legend(args.titles.split(","))
 
-plt.show()
+if args.imgname:
+    plt.savefig(args.imgname)
+else:
+    plt.show()