Remove gosu in favour of alpines iputils-ping

[CRCinAU]

Not only is the iputils-ping package smaller, it correctly works within a docker container.

The side effect of removing gosu is that docker containers built without it show ~52 fewer security vulnerabilities without the gosu binary installed.

While the author of gosu says this isn't a problem anyway, its just a bad practice. As such, we end up with a smaller window for issues, and a smaller container size as a bonus.

[manios]

Ηι @CRCinAU !

Thank you for your contribution! At the moment I cannot merge it because the package is not available in Alpine 3.12 as you can see here. As soon as #45 is unblocked we will test and merge it .

Thanks!

[CRCinAU]

Ah - I totally missed this as I only run on x86_64 - so I bumped all the way to alpine:edge because I use perl-string-random that doesn't seem to appear in anything else. In reality, I probably should just fix that perl code I use for checking a SIP service to generate a random string without using String::Random.

I'm not sure I have an arm system I can test things beyond alpine:3.12 to confirm your findings, but I'll see what I can do...