cmd/scollector: Allow specifying no host
cmd/scollector: Allow specifying no host

This requires changing the semantics of tags to copy and create a new map.

eMerzh/bosun,csmith-palantir/bosun,vimeo/bosun,gregdel/bosun,bridgewell/bosun,eMerzh/bosun,jareksm/bosun,Skyscanner/bosun,GROpenSourceDev/bosun,objStorage/bosun,treejames/bosun,dimamedvedev/bosun,alienth/bosun,briantist/bosun,dieface/bosun,dieface/bosun,GROpenSourceDev/bosun,csmith-palantir/bosun,eMerzh/bosun,CheRuisiBesares/bosun,couchand/bosun,shanemadden/bosun,Skyscanner/bosun,csmith-palantir/bosun,bosun-monitor/bosun,dieface/bosun,melifaro/bosun,evgeny-potapov/bosun,bookingcom/bosun,inkel/bosun,cazacugmihai/bosun,cyngn/bosun,trigrass2/bosun,bridgewell/bosun,augporto/bosun,youngl98/bosun,cazacugmihai/bosun,objStorage/bosun,snowsnail/bosun,GROpenSourceDev/bosun,mnikhil-git/bosun,influxdata/bosun,mehulkar/bosun,seekingalpha/bosun,influxdb/bosun,mnikhil-git/bosun,alienth/bosun,noblehng/bosun,mhenderson-so/bosun,dbirchak/bosun,treejames/bosun,bookingcom/bosun,youngl98/bosun,shanemadden/bosun,briantist/bosun,melifaro/bosun,madhukarreddy/bosun,noblehng/bosun,influxdata/bosun,mathpl/bosun,objStorage/bosun,mhenderson-so/bosun,cyngn/bosun,objStorage/bosun,Skyscanner/bosun,TrentScholl/bosun,mehulkar/bosun,objStorage/bosun,snowsnail/bosun,inkel/bosun,gregdel/bosun,yyljlyy/bosun,simnv/bosun,bookingcom/bosun,inkel/bosun,influxdb/bosun,mhenderson-so/bosun,jareksm/bosun,noblehng/bosun,gregdel/bosun,madhukarreddy/bosun,vitorboschi/bosun,vimeo/bosun,madhukarreddy/bosun,augporto/bosun,inkel/bosun,alienth/bosun,azhurbilo/bosun,yyljlyy/bosun,snowsnail/bosun,augporto/bosun,seekingalpha/bosun,Skyscanner/bosun,simnv/bosun,Dieterbe/bosun,mehulkar/bosun,mathpl/bosun,jareksm/bosun,azhurbilo/bosun,Skyscanner/bosun,bridgewell/bosun,azhurbilo/bosun,yyljlyy/bosun,noblehng/bosun,bridgewell/bosun,objStorage/bosun,bosun-sharklasers/bosun,azhurbilo/bosun,bosun-monitor/bosun,jareksm/bosun,dimamedvedev/bosun,mathpl/bosun,snowsnail/bosun,bosun-monitor/bosun,mxk1235/bosun,dimamedvedev/bosun,Dieterbe/bosun,mxk1235/bosun,influxdb/bosun,TrentScholl/bosun,augporto/bosun,leapar/bosun,madhukarreddy/bosun,seekingalpha/bosun,youngl98/bosun,youngl98/bosun,TrentScholl/bosun,fisdap/bosun,simnv/bosun,cyngn/bosun,cazacugmihai/bosun,bosun-monitor/bosun,leapar/bosun,dbirchak/bosun,briantist/bosun,briantist/bosun,evgeny-potapov/bosun,mhenderson-so/bosun,mehulkar/bosun,couchand/bosun,augporto/bosun,evgeny-potapov/bosun,mnikhil-git/bosun,simnv/bosun,bookingcom/bosun,briantist/bosun,cyngn/bosun,mehulkar/bosun,SlashmanX/bosun,SlashmanX/bosun,snowsnail/bosun,briantist/bosun,couchand/bosun,shanemadden/bosun,cazacugmihai/bosun,influxdata/bosun,dbirchak/bosun,melifaro/bosun,GROpenSourceDev/bosun,yyljlyy/bosun,treejames/bosun,vitorboschi/bosun,fisdap/bosun,cazacugmihai/bosun,treejames/bosun,leapar/bosun,melifaro/bosun,TrentScholl/bosun,vimeo/bosun,vitorboschi/bosun,yyljlyy/bosun,influxdb/bosun,seekingalpha/bosun,dbirchak/bosun,bookingcom/bosun,youngl98/bosun,mnikhil-git/bosun,trigrass2/bosun,mathpl/bosun,jareksm/bosun,leapar/bosun,madhukarreddy/bosun,CheRuisiBesares/bosun,fisdap/bosun,SlashmanX/bosun,eMerzh/bosun,melifaro/bosun,bosun-monitor/bosun,influxdb/bosun,dbirchak/bosun,azhurbilo/bosun,inkel/bosun,dieface/bosun,cyngn/bosun,SlashmanX/bosun,bosun-sharklasers/bosun,gregdel/bosun,snowsnail/bosun,trigrass2/bosun,TrentScholl/bosun,cyngn/bosun,TrentScholl/bosun,mxk1235/bosun,bosun-sharklasers/bosun,dimamedvedev/bosun,cazacugmihai/bosun,bosun-sharklasers/bosun,fisdap/bosun,bosun-monitor/bosun,yyljlyy/bosun,mhenderson-so/bosun,eMerzh/bosun,treejames/bosun,gregdel/bosun,trigrass2/bosun,Dieterbe/bosun,csmith-palantir/bosun,alienth/bosun,trigrass2/bosun,seekingalpha/bosun,azhurbilo/bosun,youngl98/bosun,CheRuisiBesares/bosun,mnikhil-git/bosun,influxdb/bosun,vitorboschi/bosun,influxdata/bosun,dbirchak/bosun,mnikhil-git/bosun,leapar/bosun,bookingcom/bosun,mxk1235/bosun,fisdap/bosun,noblehng/bosun,mehulkar/bosun,inkel/bosun,CheRuisiBesares/bosun,madhukarreddy/bosun,dieface/bosun,mxk1235/bosun,dimamedvedev/bosun,CheRuisiBesares/bosun,bridgewell/bosun,csmith-palantir/bosun,fisdap/bosun,Dieterbe/bosun,shanemadden/bosun,trigrass2/bosun,shanemadden/bosun,dimamedvedev/bosun,evgeny-potapov/bosun,vimeo/bosun,influxdata/bosun,simnv/bosun,treejames/bosun,melifaro/bosun,simnv/bosun,dieface/bosun,augporto/bosun,mathpl/bosun,seekingalpha/bosun,evgeny-potapov/bosun,bosun-sharklasers/bosun,gregdel/bosun,CheRuisiBesares/bosun,eMerzh/bosun,GROpenSourceDev/bosun,SlashmanX/bosun,couchand/bosun,bosun-sharklasers/bosun,Skyscanner/bosun,alienth/bosun,mxk1235/bosun,couchand/bosun,influxdata/bosun,csmith-palantir/bosun,mhenderson-so/bosun,vitorboschi/bosun,alienth/bosun,shanemadden/bosun,mathpl/bosun,vitorboschi/bosun,GROpenSourceDev/bosun,couchand/bosun,leapar/bosun,jareksm/bosun,noblehng/bosun,evgeny-potapov/bosun,SlashmanX/bosun,bridgewell/bosun