Adding regression tests.

Currently coverings for datastore.

@rakyll if the approach is ok I'll add to the README instructions on how to run the tests (basically configuring the export variables in run_regression_tests.sh) and I will add the tests to our build.
I don't understand fully why we're interested in the value of specific indices?

var firstKey = keys[0];
var secondKey = keys[1];

We can assert the lengths of key1 and key2. Then make a getAll, and deepEqual(objs[0], post1) and so on.