add Client Metadata "appName" in Audit message output

2018-07-30T15:04:43.873+0000 I COMMAND  [conn65251] command admin.$cmd appName: "Robomongo" command: isMaster { isMaster: 1, client: { application: { name: "Robomongo" }, driver: { name: "MongoDB Internal Client", version: "3.4.3-7-gf394f8c" }, os: { type: "Windows", name: "Microsoft Windows 8", architecture: "x86_64", version: "6.2 (build 9200)" } }, $db: "admin" } numYields:0 reslen:891 locks:{} protocol:op_query 0ms