log: Add ability to specify format strings
log: Add ability to specify format strings

This adds log --format=<str>

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