Change TestSecurityConfigUpdateRootCA test to use a custom GRPC dialer that can surface TLS handshake errors, which GRPC considers transient.
Change TestSecurityConfigUpdateRootCA test to use a custom GRPC dialer that
can surface TLS handshake errors, which GRPC considers transient.

Signed-off-by: Ying Li <f39392f1e2d21dabc2bc5ab11d2bf832bde87b60@docker.com>

dperny/swarmkit-1,docker/swarmkit,docker/swarmkit,dperny/swarmkit-1