Allow access to CurrentAttributes in test teardown

[etiennebarrie]

Summary

When using CurrentAttributes in tests, they get reset before teardown.
It's annoying when you use multiple setup/teardown in different places and expect to be able to use CurrentAttributes.

For example:

AccountTestHelper
  setup: Current.account = Account.first

SomeTest
  setup: Redis.current.set("account:#{Current.account.id}", Current.account.data)
  teardown: Redis.current.del("account:#{Current.account.id}") # Current.account has already been reset

Since the test helper helps to prevent leaks, it can call reset_all at the very end of teardown, in after_teardown, after the call to super.

@rafaelfranca
cc @byroot