PROBLEM
========
While upgrading a table using generated columns from 5.7 to
8.x, if the column expression is invalid, e.g due to
deprecated functions such as password() or des_encrypt(),
the error message mentions only the table name. It would be
more useful to also mention the column name and the
expression used.

ANALYSIS
========
The error was being logged in migrate_table_to_dd() after
returning from the call to
fix_generated_columns_for_upgrade(). In order to determine
the exact column and expression for which it failed, the
error should be logged within
fix_generated_columns_for_upgrade() instead. However, in
order to avoid changing the existing error message, a new
log error message should be created for this requirement.

FIX
========
This patch adds a new error log message on the server which
includes both the column (field_name) and the expression
(expr_str) of the generated column for which the upgrade
failed. To get this information, the LogErr() function call
was added to the point at which the upgrade fails, i.e.
within fix_generated_columns_for_upgrade().

Change-Id: Ib8d35e9f28d5735edca7baeb98103b8063266ec4