Build fix: nocrypto moved to mirage-solo5; unsupported Xen on 4.03 dropped from CI matrix; application/dns package updates

[olleolleolle]

@hannesm this is the smallest-possible try to fix the build.

"ocamlfind: Package `nocrypto.mirage' not found”

This was about a moved package, nocrypto. It moved from ocaml-freestanding to mirage-solo5.

Our config.ml for that

A PR elsewhere that does the same change

xen on 4.03 removed from CI matrix

This OCaml version is not supported, right now.

application/dns package updates

[hannesm]

regarding the second item: MirageOS on Xen and 4.03 is these days no longer supported:

• @avsm removed in mirage-xen-ocaml 3.0.4 removed OCaml 4.03 support in mirage/mirage-platform@8f79fcb
• @samoht required since mirage 3.0.5 the minimal mirage-xen-ocaml version to be 3.0.4 mirage/mirage@a78bc0c
  --> Xen + MirageOS is 4.04.2 only for now (is this intended? should it be more prominently be shown?)

[hannesm]

thanks for fixing the examples and the travis job here!

[olleolleolle]

Thanks for the help and the trust! \o/