Use Ping API in wallet gRPC client

[b00f]

Currently, in the Wallet gRPC client, we use the GetBlockchainInfo API. After fixing issue #1888, we can now replace it with the Ping API.

[Chesblaw]

@b00f hi please assign me

[b00f]

@Chesblaw Please go ahead, remember we need it in version 1.11.0 (the next version)