Improve error message for compiler errors on commands

[fhunleth]

Here's an example:

$ ssh nerves.local 'cmd("ls")'
**Error** ** (CompileError) nofile: cannot compile file (errors have been logged)
    (elixir 1.17.2) src/elixir.erl:455: :elixir.quoted_to_erl/4
    (elixir 1.17.2) src/elixir.erl:332: :elixir.eval_forms/4
    (elixir 1.17.2) lib/module/parallel_checker.ex:112: Module.ParallelChecker.verify/1
    (elixir 1.17.2) lib/code.ex:572: Code.validated_eval_string/3
    (nerves_ssh 1.0.0) lib/nerves_ssh/exec.ex:23: NervesSSH.Exec.run/1
    (ssh 5.2.1) ssh_cli.erl:828: anonymous fn/4 in :ssh_cli.exec_in_self_group/5

The errors were logged, but it would be nice it they were returned. It would be nicer if the result looked like this:

$ ssh nerves.local 'cmd("ls")'
error: undefined function cmd/1 (there is no such import)
└─ iex:1

** (CompileError) cannot compile code (errors have been logged)