AiopgInstrumentor: aiopg.connect() failure with AttributeError: __aexit__

[pocman]

Describe your environment
Ubuntu, python 3.6, aiopg 1.0.0, opentelemetry 0.16b1

Steps to reproduce
On a working flask application using aiopg like here to https://github.com/miguelgrinberg/python-web-perf/blob/master/src/async_db.py

from opentelemetry import trace
from opentelemetry.exporter import zipkin
from opentelemetry.instrumentation.flask import FlaskInstrumentor
from opentelemetry.sdk.trace import TracerProvider
from opentelemetry.sdk.trace.export import BatchExportSpanProcessor
from opentelemetry.instrumentation.aiohttp_client import create_trace_config
from opentelemetry.instrumentation.aiopg import AiopgInstrumentor

asyncio.set_event_loop_policy(uvloop.EventLoopPolicy())
loop = asyncio.get_event_loop()

app = flask.Flask("python-web-perf")

# opentelemetry
trace.set_tracer_provider(TracerProvider())
zipkin_exporter = zipkin.ZipkinSpanExporter(
    service_name="app_asyncio_flask",
    url=f'http://{zipkin_host}:9411/api/v2/spans',
)
trace.get_tracer_provider().add_span_processor(
    BatchExportSpanProcessor(zipkin_exporter)
)

app = flask.Flask(__name__)
FlaskInstrumentor().instrument_app(app)
AiopgInstrumentor().instrument()

What is the expected behavior?
I expect the postgresql span to be available in zipkin.

What is the actual behavior?

The aiopg.connect call fail with the following exception.

Traceback (most recent call last):
  File "/home/tpocreau/.venv/web-perf/lib/python3.6/site-packages/flask/app.py", line 2447, in wsgi_app
    response = self.full_dispatch_request()
  File "/home/tpocreau/.venv/web-perf/lib/python3.6/site-packages/flask/app.py", line 1952, in full_dispatch_request
    rv = self.handle_user_exception(e)
  File "/home/tpocreau/.venv/web-perf/lib/python3.6/site-packages/flask/app.py", line 1821, in handle_user_exception
    reraise(exc_type, exc_value, tb)
  File "/home/tpocreau/.venv/web-perf/lib/python3.6/site-packages/flask/_compat.py", line 39, in reraise
    raise value
  File "/home/tpocreau/.venv/web-perf/lib/python3.6/site-packages/flask/app.py", line 1950, in full_dispatch_request
    rv = self.dispatch_request()
  File "/home/tpocreau/.venv/web-perf/lib/python3.6/site-packages/flask/app.py", line 1936, in dispatch_request
    return self.view_functions[rule.endpoint](**req.view_args)
  File "/home/tpocreau/wk/python-web-perf/src/app_asyncio_flask.py", line 76, in test
    fetch(feature_store_url),
  File "uvloop/loop.pyx", line 1456, in uvloop.loop.Loop.run_until_complete
  File "/home/tpocreau/wk/python-web-perf/src/async_db.py", line 11, in get_row
    async with aiopg.connect(database='test', user='test', password='test', host=pg_host) as conn:
AttributeError: __aexit__

Without the AiopgInstrumentor().instrument() line, the application is running as expected.

Additional context
I replaced aiopg by asyncpg, and everything is working as expected (span is available in zipkin).

async def get_row_asyncpg():
    conn = await asyncpg.connect(user='test', password='test',
                                 database='test', host=pg_host)
    index = random.randint(1, max_n)
    values = await conn.execute(
        f'select pg_sleep({delay}); select a, b from test where a = {index}'
    )
    await conn.close()
    return values

[pocman]

cc @sartx