Improve Wallet coverage (#2385)

* Add trait for RpcRequestHandler trait for RpcClient and add MockRpcClient for unit tests

* Add request_airdrop integration test

* Add timestamp_tx, witness_tx, and cancel_tx to wallet integration tests; add wallet integration tests to test-stable

* Add test cases

* Ignore plentiful sleeps in unit tests

wallet/src/main.rs

@@ -1,9 +1,7 @@
-mod wallet;
-
-use crate::wallet::{parse_command, process_command, WalletConfig, WalletError};
 use clap::{crate_version, App, Arg, ArgMatches, SubCommand};
 use solana::socketaddr;
 use solana_sdk::signature::{gen_keypair_file, read_keypair, KeypairUtil};
+use solana_wallet::wallet::{parse_command, process_command, WalletConfig, WalletError};
 use std::error;
 use std::net::SocketAddr;
 
@@ -53,6 +51,7 @@ pub fn parse_args(matches: &ArgMatches<'_>) -> Result<WalletConfig, Box<dyn erro
         timeout,
         proxy,
         drone_port: None,
+        rpc_client: None,
     })
 }