Implement missing context methods

Fixes #321

Author: ocelotl

instrumentation/opentelemetry-instrumentation-grpc/src/opentelemetry/instrumentation/grpc/_server.py

@@ -29,7 +29,7 @@
 from opentelemetry import trace
 from opentelemetry.context import attach, detach
 from opentelemetry.propagate import extract
-from opentelemetry.trace.propagation.textmap import DictGetter
+from opentelemetry.propagators.textmap import DictGetter
 from opentelemetry.trace.status import Status, StatusCode
 
 logger = logging.getLogger(__name__)

instrumentation/opentelemetry-instrumentation-grpc/src/opentelemetry/instrumentation/grpc/grpcext/_interceptor.py

@@ -232,11 +232,11 @@ def close(self):
 
     def __enter__(self):
         """Enters the runtime context related to the channel object."""
-        raise NotImplementedError()
+        return self
 
     def __exit__(self, exc_type, exc_val, exc_tb):
         """Exits the runtime context related to the channel object."""
-        raise NotImplementedError()
+        self.close()
 
 
 def intercept_channel(channel, *interceptors):