Always execute commands and prelude in subshell
    
    Before the fix the prelude was executed in main shell and commands were
    executed in nested shell only when they were passed as a string, not as a
    list.
    This approach produces problem with some  installations
    (particularly Cygwin) which have
    /etc/bash.bash_logout file  containing invocation of "/usr/bin/clear".
    This file is executed when user logs out. When run_command() sends
    "exit" command to remote shell, "clear" returns exit code 1 complaining
    about TERM variable not being defined, which is normal for non-interactive
    sessions. Without "set -e" option this is handled correctly and shell
    returns result code of last executed user command. But with "set -e" shell
    terminates prematurely and when user command succeeded we receive exit
    status 1.
    
    Executing "set -e" and user commands inside subshell solves both problems.
    
    Also adding test for the described scenario.