The bootSound script started to hang on strings /dev/urandom,
so replace it with a cleaner random number generation.
24134 could be used for bash, but this would make the script
less generic, as it is not available in POSIX.
Use awk random() from a suggestion from ShellCheck.
Remove the code that was there to control the parsing from
/dev/urandom.
Other fixes :
- Use wc rather than grep to count the files
- Use a subshell for proper directory handling
