tests/view_schema_test: fix flakiness caused by missing eventually()
tests/view_schema_test: fix flakiness caused by missing eventually()

All tests that involve writing to a base table and then reading from the
view table must use the eventually() function to account for the fact that
the view update is asynchronous, and may be visible only some time after
writing the base table. Forgetting an eventually() can cause the test
to become flaky and sometimes fail because the expected data is not *yet*
in the view. Botond noticed these failures in practice in two subtests
(test_partition_key_filtering_with_slice and
test_clustering_key_in_restrictions).

This patch fixes both tests, and I also reviewed the entire source file
view_schem_test.cc and found additional places missing an eventually()
(and also places that unnecessarily used eventually() to read from the
base table), and fixed those as well.

Fixes #4212

Signed-off-by: Nadav Har'El <625169824b719df98706d88646d0aae6f368ae4d@scylladb.com>
Message-Id: <20190212121140.14679-1-625169824b719df98706d88646d0aae6f368ae4d@scylladb.com>

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