SASI related tests failing since CASSANDRA-11820

Since CASSANDRA-11820 was committed, a number of tests covering SASI have been failing. In both SASIIndexTest and SSTableFlushObserverTest, rows are built using an unsorted builder, which assumes that the columns are added in clustering order. However, in both cases, this is not true and the additional checks added to UnfilteredSerializer::serializeRowBody by CASSANDRA-11820 now trigger assertion errors and, ultimately, failing tests.

In addition, SASIIndexTest reuses a single table in multiple tests and performs its cleanup in the tear down method. When the assertion error is triggered, the tear down is not run, leaving data in the table and causing other failures in subsequent tests.

Patch to follow shortly...