no longer hard-code the icon for the executor panel
no longer hard-code the icon for the executor panel

[FIXED JENKINS-36775]

SebastienGllmt/jenkins,SebastienGllmt/jenkins,SebastienGllmt/jenkins,SebastienGllmt/jenkins,SebastienGllmt/jenkins,SebastienGllmt/jenkins,SebastienGllmt/jenkins