Description: Authentication string for sha256_password
             can contain an optional part specifying
             number of hash rounds to be performed.
             Though default is 5000, an
             authentication_string directly inserted
             in mysql.user table can contain different
             value. This may cause extra computations
             and may introduce unnecessary delay.

Solution: Fixed the maximum number of rounds allowed.
(cherry picked from commit b9e85dc240a1fce3e57c3d9a3be25eab7f9be606)