Support reset_pk_sequence!

This pull request addresses following failures reported in rails/rails#7334.
It is because Oracle enhanced adapter does not have `reset_pk_sequence!` method implemented as postgresql adapter does.

```ruby
$ ARCONN=oracle ruby -Itest test/cases/associations/inverse_associations_test.rb -n /test_parent_instance_should_be_shared_with_newly_created_child/
Using oracle
Run options: -n /test_parent_instance_should_be_shared_with_newly_created_child/ --seed 30439

# Running tests:

FF

Finished tests in 0.235511s, 8.4922 tests/s, 25.4766 assertions/s.

  1) Failure:
test_parent_instance_should_be_shared_with_newly_created_child(InverseHasOneTests) [test/cases/associations/inverse_associations_test.rb:133]:
Name of man should be the same after changes to parent instance.
Expected: "Bongo"
  Actual: "Steve"

  2) Failure:
test_parent_instance_should_be_shared_with_newly_created_child_via_bang_method(InverseHasOneTests) [test/cases/associations/inverse_associations_test.rb:144]:
Name of man should be the same after changes to parent instance.
Expected: "Bongo"
  Actual: "Steve"

2 tests, 6 assertions, 2 failures, 0 errors, 0 skips
$
```