some minor tweak, reuse the mirage-mtime.mock implementation

[hannesm]

Dear @patricoferris (and maybe @djs55 is interested as well),

I fixed the issue at moby#646 (comment) by using the mirage-mtime.mock sublibrary.

This branch now compiles, what is needed though (pending releases I guess):

• mirage-mtime.mock: add a reset : unit -> unit function mirage/mirage-mtime#2 (I'm happy to merge and release)
• https://github.com/mirage/ocaml-9p/ (I'm as well happy to cut a release if you want me to)
• Continue removal of mirage-time, now from opam and dune files mirage/ocaml-hvsock#70 (to remove the mirage-time dependency once and forall, also happy to merge and release)

So, if you agree, I'd cut releases of these three opam packages in the mirage organization (after merging the mentioned outstanding PRs).

[patricoferris]

Thanks @hannesm !

This seems sensible to me, shall I hold off until the reset function lands to merge this change in the PR ?

[hannesm]

See ocaml/opam-repository#28392 -- once that is merged, it should be good (we may want to have a lower bound { >= "5.1.0" } in the vpnkit.opam though.

[hannesm]

And while at it, the 9p release ocaml/opam-repository#28394 and hvsock ocaml/opam-repository#28393

[hannesm]

I pushed a change with the bounds, this will only work once the above mentioned opam packages have been merged into the opam-repository.

[hannesm]

Note the releases are merged in opam-repository now, so this should be fine to compile and being merged.