AttachRequestHandler should record error of attach failures.

[andxu]

AttachRequestHandler.java
try {
logger.info(String.format("Trying to attach to remote debuggee VM %s:%d .",
attachArguments.hostName, attachArguments.port));
IDebugSession debugSession = DebugUtility.attach(vmProvider.getVirtualMachineManager(),
attachArguments.hostName, attachArguments.port, attachArguments.timeout);
context.setDebugSession(debugSession);
logger.info("Attaching to debuggee VM succeeded.");
} catch (IOException | IllegalConnectorArgumentsException e) {
AdapterUtils.setErrorResponse(response, ErrorCode.ATTACH_FAILURE,
String.format("Failed to attach to remote debuggee VM. Reason: %s", e.toString()));
}

[yaohaizh]

@andxu, please update the status of this issue.

[andxu]

#68

[andxu]

Done with the PR