This series adds a generic test for schema changes that generates
various schema and data before and after an ALTER TABLE operation. It is
then used to check correctness of mutation::upgrade() and sstable
readers and lead to the discovery of #3924 and #3925.
Fixes#3925.
* https://github.com/pdziepak/scylla.git schema-change-test/v3.1
schema_builder: make member function names less confusing
converting_mutation_partition_applier: fix collection type changes
converting_mutation_partition_applier: do not emit empty collections
sstable: use format() instead of sprint()
tests/random-utils: make functions and variables inline
tests: add models for schemas and data
tests: generate schema changes
tests/mutation: add test for schema changes
tests/sstable: add test for schema changes
(cherry picked from commit 564b328b2e)