This is a requirement in order to make Bazel remote execution work. Without it
it's not guaranteed that any necessary nix paths will be available during the
build.

Any local derivation will be copied over to a specified remote nix server which
will also as a Bazel executor. This way any nix paths required during the
build, will be available.

The user will have to provide the `BAZEL_NIX_REMOTE` environment variable. This
should be the name of any entry on the SSH_CONFIG file where all the
authentication details are provided.

e.g

```bash
$ export BAZEL_NIX_REMOTE=nix-server

$ cat ~/.ssh/config
Host nix-server
  Hostname 1.2.3.4
  IdentityFile ~/.ssh/nix-server
  Port 2222
  User nix-user
```

This was done in order to simplify the processes of authentication and keep the
number of configuration options to a minimum.