Enforce maximum password length

[richp10]

The maximum password length is 16 characters - but there is no warning of this when using the tool to reset the password: so if you do not know this and reset the password with:

ipmitool -I open -U ADMIN -P ADMIN user set password 2 mypasswordoversixteen

It returns no error - but if you try and login with that password it does not work.

A simple thing that would make life for us idiots who don't read the manual easier would be to do a length check on submitted password and throw an error if it is longer than sixteen characters.

[gdttn]

Since https://github.com/ipmitool/ipmitool/pull/153/files/728efe3920a60e5f29838417b35277ca623fa40d this is now enforced to the best of ipmitool's ability (and the man page updated for clever people who do eventually read the manual before submitting a bug :) ) - does this look right to you?

There are still process issues with bmc password handling in practice but I think ipmitool now mostly does the right thing.