…lojure-emacs#3567

Fixes `cider-jack-in-clj` in tramp buffers throwing:
```
Could not start nREPL server: %s (%S)
bash: /remote/path/to/cider/clojure.sh: No such file or directory\n" "exited abnormally with code 127")
```
in cases where cider is not installed in the same directory on the
remote.

To fix this, we create temporary copy of the enrich-classpath script
named `.cider__<clojure.sh|lein.sh>__<random>` on the remote before
starting the server. The possible locations of the script are, in this
order:
- tramp-tempdir (usually "/tmp")
- clojure-project-dirj
- default-directory

If the script can't be created for any reason, the server is started with
`cider-enrich-classpath` set to nil.

Note: the temporary script will remove itself after use, but stick around when
something goes wrong before the remote process is started.

`auto-save-visited-mode` will not create any tempfiles anyways, but only
save the current file.

We don't need it (yet) and Emacs 26 does not support
`split-string-shell-command`.
Don't want to fiddle with shell-quoting unless really necessary.

…init