NULL values when there is no DEFAULT
- Merged the alter_non_null test case to alter_not_null test case.
Renamed the alter_non_null_debug to alter_not_null_debug test case
NULL values when there is no DEFAULT
Copy and inplace algorithm works similarly for
NULL to NOT NULL conversion for the following cases:
(1) strict sql mode - Should give error.
(2) non-strict sql mode - Should give warnings alone
(3) alter ignore table command. - Should give warnings alone.