The grpc-proxy test logic was assuming that the context associated to client is closed,
while in practice all tests called client.Close() without explicit context close.
The current testing strategy is complicated 2 fold:
- grpc proxy works like man-in-the middle of each Connection issues
from integration tests and its lifetime is bound to the connection.
- both connections (client -> proxy, and proxy -> etcd-server) are
represented by the same ClientV3 object instance (with substituted
implementations of KV or watcher).
The fix splits context representing proxy from context representing proxy -> etcd-server connection,
thus allowing cancelation of the proxy context.
73e5714bc5