[server][AMQPConsumer] Improve scheme completion for broker URL

If broker URL starts with "amqp://" or "amqps://", we don't complete
"amqp://" to broker URL.
[server][AMQPConsumer] Use string::compare() instead of strncmp()

Because we use C++ not C!
Merge pull request #382 from project-hatohol/hapi-json-improve-broker-url-completion

[server][AMQPConsumer] Improve scheme completion for broker URL