Lock version of Go packages

[laeti-tia]

It happens regularly during the lifetime of our Go-based packages that some dependencies are changing and requirements are not met anymore on the distros we support. This last happened with s3-benchmark and bytefmt a few days ago and was corrected in the RPM with this commit: 547bc20

This lock should be ported to Debian packaging.

And it's worth looking into whether it is better to lock all Go dependencies versions for the builds we have. Although we'll need to see when we bump those dependencies up as well. Tbd.

[laeti-tia]

After discussion, this seems to be better done in the debian/rules file the same way as in the RPM spec file. Not really advisable to generalise as it is also dependant on the distro we build on. See af4bf95