mysql_db/user: Use password for my.cnf

According to the MySQL docs[0] the password should be stored after
'password=' instead of 'pass='.

[0] http://dev.mysql.com/doc/refman/5.1/en/password-security-user.html
mysql_user: handle unnecessary GRANT revocation
Merge pull request #2175 from tyll/devel

mysql_db/user: Use password for my.cnf