Do not provide --password parameter by default

It is actually different to use the option without any value
or to omit the option. In the first case (--password) there
is a prompt for password after every command; without the
option, no password is provided, which is safe and convenient
during development, from localhost.

To get a prompt for password (which is slightly annoying though
because it is repeated for every MySQL command in the script),
an empty string can be provided as argument to the string, which
results in the option --password without any value, and thus a
prompt for password.