[script][figure] Allows a number of legend > #systems

It is used to define custom legends for dev, eval plots
4 jobs for histlegends in 10 minutes and 11 seconds (queued for 6 seconds)
Status Name Job ID Coverage
  Build
passed build_linux_27 #140497
docker

00:09:16

86.0%
passed build_linux_36 #140498
docker

00:09:14

86.0%
passed build_macosx_27 #140499
macosx

00:10:11

86.0%
passed build_macosx_36 #140500
macosx

00:09:35

86.0%