[opam-devel] OPAM Dockerfiles set OPAMSWITCH

[David Sheets]

The Docker containers described by
https://github.com/ocaml/opam-dockerfiles somehow set the OPAMSWITCH
environment variable. I haven't been able to find where or why this
variable has been set and it causes many opam commands to be more
heavyweight than necessary which makes interactive use annoying. For
instance, after switching compilers, you must run something like

```
eval `opam config env --switch=system`
```

if OPAMSWITCH is set. When is OPAMSWITCH necessary? Why? What sets it?

I'm really enjoying using the opam Docker containers because it means
that a fresh, minimal, throwaway OPAM install is just a `docker run
-it --rm -v ~/Code:/Code:rw ocaml/opam:alpine-3.3_ocaml-4.02.3 ash`
away. Thanks, avsm!