ext/psycopg2: Implement BaseInstrumentor interface

[cnnradams]

1. Implemented BaseInstrumentor interface to enable auto-instrumentation
2. Added integration tests (same tests as other db integrations)

Since the psycopg2 connection object can't have properties added to it (for example, self._db_api_integration = db_api_integration throws an error), I instead closed these properties around the tracing wrappers.

Resolves #633

[ocelotl]

Hello @cnnradams

What error do you get when you

1. Implemented BaseInstrumentor interface to enable auto-instrumentation
2. Added integration tests (same tests as other db integrations)

Since the psycopg2 connection object can't have properties added to it (for example, self._db_api_integration = db_api_integration throws an error), I instead closed these properties around the tracing wrappers.

Resolves #633

Hey, @cnnradams, what is the error you mention above?

[cnnradams]

Hello @cnnradams

What error do you get when you

1. Implemented BaseInstrumentor interface to enable auto-instrumentation
2. Added integration tests (same tests as other db integrations)

Since the psycopg2 connection object can't have properties added to it (for example, self._db_api_integration = db_api_integration throws an error), I instead closed these properties around the tracing wrappers.
Resolves #633

Hey, @cnnradams, what is the error you mention above?

postgres/test_psycopg_functional.py:44: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
../../../.tox/docker-tests/lib/python3.6/site-packages/wrapt/wrappers.py:567: in __call__
    args, kwargs)
../../opentelemetry-ext-dbapi/src/opentelemetry/ext/dbapi/__init__.py:118: in _wrap_connect
    return db_integration.wrapped_connection(wrapped, args, kwargs)
../../opentelemetry-ext-dbapi/src/opentelemetry/ext/dbapi/__init__.py:224: in wrapped_connection
    return TracedConnectionProxy(connection, self)
../../opentelemetry-ext-dbapi/src/opentelemetry/ext/dbapi/__init__.py:268: in __init__
    self._db_api_integration = db_api_integration
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

self = <TracedConnectionProxy at 0x7faae3621208 for connection at 0x7faae3928660>
name = '_db_api_integration'
value = <opentelemetry.ext.dbapi.DatabaseApiIntegration object at 0x7faae3647898>

    def __setattr__(self, name, value):
        if name.startswith('_self_'):
            object.__setattr__(self, name, value)
    
        elif name == '__wrapped__':
            object.__setattr__(self, name, value)
            try:
                object.__delattr__(self, '__qualname__')
            except AttributeError:
                pass
            try:
                object.__setattr__(self, '__qualname__', value.__qualname__)
            except AttributeError:
                pass
    
        elif name == '__qualname__':
            setattr(self.__wrapped__, name, value)
            object.__setattr__(self, name, value)
    
        elif hasattr(type(self), name):
            object.__setattr__(self, name, value)
    
        else:
>           setattr(self.__wrapped__, name, value)
E           AttributeError: 'psycopg2.extensions.connection' object has no attribute '_db_api_integration'

../../../.tox/docker-tests/lib/python3.6/site-packages/wrapt/wrappers.py:190: AttributeError

basically, you can't seem to assign new properties to objects that were originally defined in C (same issue happens with sqlite3, does not happen with mysql since its connection was defined in python)

[lzchen]

Any reason for these wrapper functions?

[cnnradams]

yes - see my above comment. tl;dr: Can't assign new properties to the psycopg2 connection object

[lzchen]

Good job using the TestBase!

[lzchen]

LGTM

[codeboten]

LGTM! Thanks for the PR