Fix enum_user_directories Duplicate Directories

[jheysel-r7]

This first part of #enum_user_directories parses /etc/passwd and adds for example /home/msfuser to the user_dirs array.

    passwd = '/etc/passwd'
    if file_exist?(passwd)
      read_file(passwd).each_line do |passwd_line|
        user_dirs << passwd_line.split(':')[5]
      end
    end

The second part #enum_user_directories runs the cmd_exec command below and adds for example/home/msfuser\n to the user_dirs array. Every directory contains a new line at the end of the string except for the last entry, which is why we've added .chomp so that the duplicate entries will now get removed by the .uniq call at the end of the method.

user_dirs << cmd_exec('ls /home').each_line.map { |l| "/home/#{l.chomp}" }

Verification

Test this in isolation or run a post module such as the new ssh_key persistence module which calls #enum_user_directories to see how it was evaluating some home directories twice before this fix. Note this wasn't causing issues but figured it should be corrected.