alternator-test: test for ConditionExpression feature
alternator-test: test for ConditionExpression feature

This patch adds a very comprehensive test for the ConditionExpression
feature, i.e., the newer syntax of conditional writes replacing
the old-style "Expected" - for the UpdateItem, PutItem and DeleteItem
operations.

I wrote these tests while closely following the DynamoDB ConditionExpression
documentation, and attempted to cover all conceivable features, subfeatures
and subcases of the ConditionExpression syntax - to serve as a test for a
future support for this feature in Alternator (see issue #5053).

As usual, all these tests pass on AWS DynamoDB, but because we haven't yet
implemented this feature in Alternator, all but one xfail on Alternator.

Refs #5053.

Signed-off-by: Nadav Har'El <625169824b719df98706d88646d0aae6f368ae4d@scylladb.com>
Message-Id: <20191229143556.24002-1-625169824b719df98706d88646d0aae6f368ae4d@scylladb.com>

scylladb/scylla,avikivity/scylla,avikivity/scylla,scylladb/scylla,scylladb/scylla,scylladb/scylla,avikivity/scylla