cmd/gendb: failure function does formatting
cmd/gendb: failure function does formatting

Rename `fail` to `failf` and have it take a format string and args
like printf-style functions.

Change-Id: Ifd363e372b40ed3da38fa3e3c82a966f65ced587
Reviewed-on: https://go-review.googlesource.com/c/vulndb/+/352749
Trust: Jonathan Amsterdam <e3d3698b2ccd5955e4adf250d0785062d0f9018b@google.com>
Run-TryBot: Jonathan Amsterdam <e3d3698b2ccd5955e4adf250d0785062d0f9018b@google.com>
TryBot-Result: Go Bot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Roland Shoemaker <0d270388f2f92757a5de0f4bd891d3b392c44c4f@golang.org>

golang/vuln,golang/vuln