~~This port is not allowed to build a package, so no poudriere tests~~
~~for this port. I just installed it on 12.0-ALPHA6 i386/amd64 manually~~
~~and ran `linux-vdbench -t`, it works.~~
Proposed commit log message:
```
[NEW PORT]: benchmarks/linux-vdbench: Command line disk I/O benchmark utility
Vdbench is a command line utility specifically created to help
engineers and customers generate disk I/O workloads to be used
for validating storage performance and storage data integrity.
WWW: http://www.oracle.com/technetwork/server-storage/vdbench-downloads-1901681.html
Reviewed_by: koobs, mat
Approved by: koobs (mentor)
Differential_Revision: D17255
```