This change makes the etcd package compatible with the existing Go
ecosystem for module versioning.
Used this tool to update package imports:
https://github.com/KSubedi/gomove
gRPC has moved the transport package to an internal-only directory. This
eliminates direct use of the transport package in the stress test in
favor of the error code from gRPC that represents a connection problem.
https://godoc.org/google.golang.org/grpc/internal/transport is the new
location for the package, which says it's not intended to be imported
directly. Instead, the maintainers suggested to use the code Unavailable
to detect a connection problem.
This change slightly reorganizes the stresser test error handling.
