Examples: Access the default VHost not possible

[roe85]

Describe the bug
Its not possible to access the default vhost with e.g. rmqhelloworld_producer

To Reproduce
Steps to reproduce the behavior:

1. Call rmqhelloworld_producer amqp://guest:guest@localhost:5672/
2. See Error: Error: Connection error NOT_ALLOWED - vhost not found, rc: 530

Expected behavior
It would not use "" as vhost but rather the default "/" vhost

Additional context
Could be fixed in ConnectionString::parseParts function or Within the getter SimpleEndpoint::vhost by using / as vhost if it is empty.