dt/dl: Integration testing for schema compat integration

test that:
- table schema updates work
- valid evolved schemas are backwards compatible w/ historical rows
- adding columns never results in reading pre-existing values from another column
- removing a column and adding it back in a subsequent update creates a NEW
  column that does not collide with the old 'version'
- attempting to read from a dropped column fails gracefully
- changing the order of columns doesn't change the values associated with the
  a column or field name

Signed-off-by: Oren Leiman <[email protected]>