libhdfs++: Add appropriate catch blocks for ASIO operations that throw

libhdfs++ doesn't create exceptions of its own but it should be able to gracefully handle exceptions thrown by libraries it uses, particularly asio.

libhdfs++ should be able to catch most exceptions within reason either at the call site or in the code that spins up asio worker threads. Certain system exceptions like std::bad_alloc don't need to be caught because by that point the process is likely in a unrecoverable state.