Added usage for graceful_stop in drillbit.sh
Added usage for graceful_stop in drillbit.sh

closes #1135

Ben-Zvi/drill,mapr/incubator-drill,parthchandra/drill,sohami/drill,apache/drill,apache/drill,sohami/drill,cchang738/drill,kkhatua/drill,vvysotskyi/drill,arina-ielchiieva/drill,nagix/drill,paul-rogers/drill,ppadma/drill,superbstreak/drill,parthchandra/drill,pwong-mapr/incubator-drill,mapr/incubator-drill,tgrall/drill,tgrall/drill,Ben-Zvi/drill,johnnywale/drill,cchang738/drill,pwong-mapr/incubator-drill,paul-rogers/drill,kkhatua/drill,vvysotskyi/drill,Ben-Zvi/drill,ppadma/drill,sohami/drill,apache/drill,Agirish/drill,kkhatua/drill,sohami/drill,tgrall/drill,ppadma/drill,pwong-mapr/incubator-drill,nagix/drill,Agirish/drill,vvysotskyi/drill,vvysotskyi/drill,arina-ielchiieva/drill,Agirish/drill,parthchandra/drill,johnnywale/drill,johnnywale/drill,cchang738/drill,ppadma/drill,superbstreak/drill,vdiravka/drill,paul-rogers/drill,parthchandra/incubator-drill,vvysotskyi/drill,vdiravka/drill,superbstreak/drill,parthchandra/incubator-drill,parthchandra/drill,parthchandra/incubator-drill,pwong-mapr/incubator-drill,nagix/drill,mapr/incubator-drill,superbstreak/drill,kkhatua/drill,arina-ielchiieva/drill,paul-rogers/drill,Ben-Zvi/drill,Agirish/drill,apache/drill,apache/drill,arina-ielchiieva/drill,mapr/incubator-drill,cchang738/drill,vvysotskyi/drill,Agirish/drill,vdiravka/drill,mapr/incubator-drill,kkhatua/drill,tgrall/drill,vdiravka/drill,nagix/drill,nagix/drill,superbstreak/drill,parthchandra/incubator-drill,parthchandra/drill,paul-rogers/drill,sohami/drill,cchang738/drill,superbstreak/drill,johnnywale/drill,Agirish/drill,sohami/drill,Ben-Zvi/drill,mapr/incubator-drill,arina-ielchiieva/drill,ppadma/drill,paul-rogers/drill,Ben-Zvi/drill,vdiravka/drill,kkhatua/drill,parthchandra/incubator-drill,pwong-mapr/incubator-drill,tgrall/drill,arina-ielchiieva/drill,nagix/drill,cchang738/drill,ppadma/drill,pwong-mapr/incubator-drill,parthchandra/drill,apache/drill,johnnywale/drill