While debugging build failures (regardless if the problem lies in
the package built or in sbuild) it would be useful if the produced
build log would show, how sbuild was invoked.

As an example, if I run `PERL5LIB=./lib bin/sbuild --dist=stable
--run-autopkgtest hello` then I'd like to see `--dist=stable 
--run-autopkgtest hello` in the build log.

Similarly, if I pass `dpkg_1.22.21.dsc` to sbuild, I'd like to see
`dpkg_1.22.21.dsc` in the build log.

Thanks,
Chris