cmd/scollector: Fix bug in AWS billing collector. (#2156)
cmd/scollector: Fix bug in AWS billing collector. (#2156)

The billing collector did not correctly account for Route 53 zone billing
where the bill contains an empty zone name.

This fixes issue #2147
bookingcom/bosun,bookingcom/bosun,mhenderson-so/bosun,bosun-monitor/bosun,bookingcom/bosun,bookingcom/bosun,bookingcom/bosun,bosun-monitor/bosun,mhenderson-so/bosun,bosun-monitor/bosun,mhenderson-so/bosun,mhenderson-so/bosun,mhenderson-so/bosun,bookingcom/bosun,mhenderson-so/bosun,bosun-monitor/bosun,bosun-monitor/bosun,bosun-monitor/bosun