cmd/tsdbrelay: switch to slog for future Event Log support. Also improve log and verbose messages.
cmd/tsdbrelay: switch to slog for future Event Log support. Also improve log and verbose messages.

alienth/bosun,bookingcom/bosun,mhenderson-so/bosun,leapar/bosun,simnv/bosun,melifaro/bosun,csmith-palantir/bosun,seekingalpha/bosun,leapar/bosun,mhenderson-so/bosun,csmith-palantir/bosun,mhenderson-so/bosun,leapar/bosun,bosun-monitor/bosun,mhenderson-so/bosun,melifaro/bosun,csmith-palantir/bosun,seekingalpha/bosun,bookingcom/bosun,simnv/bosun,csmith-palantir/bosun,bosun-monitor/bosun,mhenderson-so/bosun,alienth/bosun,simnv/bosun,leapar/bosun,alienth/bosun,bosun-monitor/bosun,bookingcom/bosun,melifaro/bosun,leapar/bosun,csmith-palantir/bosun,simnv/bosun,mhenderson-so/bosun,bosun-monitor/bosun,bookingcom/bosun,simnv/bosun,bosun-monitor/bosun,simnv/bosun,bookingcom/bosun,melifaro/bosun,melifaro/bosun,alienth/bosun,melifaro/bosun,alienth/bosun,seekingalpha/bosun,seekingalpha/bosun,csmith-palantir/bosun,bosun-monitor/bosun,alienth/bosun,leapar/bosun,bookingcom/bosun,seekingalpha/bosun,seekingalpha/bosun