Fix alter table metadata lose data

Fix a bug in the `BasicDDLFunctions#alterTableRemoveOldStorage()` which, if the alter table didn't change the table and require moving the data for the table (i.e. a METADATA only change), would delete the data anyways. 

Update the AlterTableCAOIIT test to include data checks as well as schema structure checks. 
Why not check the changeLevel instead of checking parent unique keys?