Stop using icecc-create-env to build environments

[mystor]

I mentioned to @luser that I had whipped up my own create-env system within sccache-dist, due to icecc-create-env not working well for me.

Not sure how well this works, but it can probably at least act as a starting point.

[jrmuizel]

review ping

[jrmuizel]

@mystor also it looks like this doesn't build.

[mystor]

Hmm - can't build it locally again due to the build system being unable to find openssl, but here's a fix hopefully(?)

[aidanhs]

This looks good to me. I've made a PR to this branch to fix the build failures at mystor#1. It also needs a rebase, but the only conflict is a use line.

Alternatively, I'm happy to do the rebasing and create a new PR. Whatever is easiest.

[luser]

It looks like this needs to be rebased to latest master. Do one of you want to take care of that or should I do it?

[mystor]

If there's any chance you'd be willing to do that it would save me setting stuff up again :-)

[luser]

I rebased this locally and pushed it to master:
06421ba

Thanks!