samples: Update spanning_tree sample
samples: Update spanning_tree sample

MurphyMc/pox,jacobq/csci5221-viro-project,diogommartins/pox,denovogroup/pox,waltznetworks/pox,PrincetonUniversity/pox,waltznetworks/pox,waltznetworks/pox,VamsikrishnaNallabothu/pox,denovogroup/pox,pthien92/sdn,waltznetworks/pox,chenyuntc/pox,diogommartins/pox,adusia/pox,MurphyMc/pox,MurphyMc/pox,pthien92/sdn,adusia/pox,pthien92/sdn,denovogroup/pox,denovogroup/pox,noxrepo/pox,diogommartins/pox,VamsikrishnaNallabothu/pox,noxrepo/pox,kavitshah8/SDNDeveloper,carlye566/IoT-POX,carlye566/IoT-POX,noxrepo/pox,PrincetonUniversity/pox,andiwundsam/_of_normalize,kavitshah8/SDNDeveloper,adusia/pox,kulawczukmarcin/mypox,adusia/pox,VamsikrishnaNallabothu/pox,carlye566/IoT-POX,kulawczukmarcin/mypox,jacobq/csci5221-viro-project,waltznetworks/pox,andiwundsam/_of_normalize,diogommartins/pox,PrincetonUniversity/pox,kpengboy/pox-exercise,kpengboy/pox-exercise,carlye566/IoT-POX,jacobq/csci5221-viro-project,kulawczukmarcin/mypox,MurphyMc/pox,kulawczukmarcin/mypox,jacobq/csci5221-viro-project,xAKLx/pox,andiwundsam/_of_normalize,chenyuntc/pox,chenyuntc/pox,pthien92/sdn,chenyuntc/pox,noxrepo/pox,xAKLx/pox,VamsikrishnaNallabothu/pox,xAKLx/pox,andiwundsam/_of_normalize,denovogroup/pox,jacobq/csci5221-viro-project,xAKLx/pox,kavitshah8/SDNDeveloper,kpengboy/pox-exercise,kavitshah8/SDNDeveloper,kulawczukmarcin/mypox,kpengboy/pox-exercise,pthien92/sdn,MurphyMc/pox,xAKLx/pox,diogommartins/pox,VamsikrishnaNallabothu/pox,kpengboy/pox-exercise,PrincetonUniversity/pox,adusia/pox,carlye566/IoT-POX,PrincetonUniversity/pox,chenyuntc/pox