This is basically a copy of the existing test_abort but passes
trailing_metadata. This test fails because the `code()` and `details()`
from the returned exception are masking the actual abort reason due to
the bug.

This adds a separate ServicerContext for the grpc.aio interceptor to
use that inherits from the correct grpc.aio.ServicerContext. Previously
it was ultimately using grpc.ServicerContext where the abort method has
a different signature to what should have been in use.

Using wrapt eliminates a bunch of the boilerplate associated with
inheriting from grpc.aio.ServicerContext directly. It also means that if
methods are added or their signatures change, there will only be a
breaking change for abort, set_code, or set_details.