composer: seed the random number generator

[ondrejbudai]

I thought rand in Go is auto-seeded but I was wrong, see [1].
This commit adds seed initialization.

[1]: https://golang.org/pkg/math/rand/#Seed

[bcl]

Where is math/rand being used? I see crypto/rand being used in several places but not math/rand -- they are different :) crypto/rand gets its numbers from getrandom or /dev/urandom and is much better than math/rand which, even with it seeded, has a higher chance of collisions between systems (unlikely with the uses of Nano but still possible if a number of systems all start at the same time).

[ondrejbudai]

I added math/rand here: #1131 I guess I can seed the Manifest() function with crypto/rand...

[ondrejbudai]

I force-pushed a version with crypto/rand. The global rand.Seed() call that I had before was ugly, I think this is nicer.

[teg]

Nice! I agree with Brian, nice to use proper random seed, even if it would not really make a difference for this usecase.

[bcl]

Ha, I was looking at the wrong branch when searching for math/rand use :) Looks good to me.

[ondrejbudai]

osbuild/koji-osbuild#54 and #1135 appeared, otherwise we're green. 💚