protobuf-rpc: added and ability to check server connect availability

Signed-off-by: Ketoth Xupack <ketoth.xupack@gmail.com>
protobuf-rpc: additional checks in integrational scenario

Signed-off-by: Ketoth Xupack <ketoth.xupack@gmail.com>
protobuf-rpc: better comments/method names for client interface

Signed-off-by: Ketoth Xupack <ketoth.xupack@gmail.com>