test/alternator: make test_ttl.py tests fast on Alternator
test/alternator: make test_ttl.py tests fast on Alternator

The tests for the TTL feature in test/alternator/test_ttl.py takes huge
amount of time on DynamoDB - 10 to 30 minutes (!) - because it delays
expiration of items a long time after their intended expiration times.

We intend Scylla's implementation to have a configurable delay for the
expiration scanner, which we will be able to configure to very short
delays for tests. So These tests can be made much faster on Scylla.
So in this patch we change all of the tests to finish much more quickly
on Scylla.

Many of the tests still fail, because the TTL feature is not implemented
yet.

Although after this change all the tests in test_ttl.py complete in
a reasonable amount of time (around 3 seconds each), we still mark
them as "veryslow" and the "--runveryslow" flag is needed to run them.
We should consider changing this in the future, so that these tests will
run as part of our default test suite.

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

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