Fixes for running Oracle Integration tests.

Added null checks for object name.
Oracle doesn't support setting a sequence as a default value so removed oracle from that test.
After the Diff refactoring, CreateTableChange is not having its columns serialized.
Added overridden methods to CreateTableChange to return columns as a serializable field.
There might be a more elegant way to do this. It looks like I should have a getter and setter
for columns to be picked up automatically as a serilizable value.

I also encountered weird behavior with Oracle whereby an overly long description was correctly
limited to 255 characters but was for some reason being treated as 259 characters by oracle.
This thus resulted in a constraint violation as the length was then too long for the description.
Bit of a hack but I lowered the description length to 250 and that seems to work.