Put all alternative configurations in default trove.conf

Now we copy-and-paste /etc/trove/trove.conf.example to deploy trove and it doesn't work because we miss some configurations.

Take trove-guestagent for example, we have to set "datastore_manager" as mysql or redis before starting guestagent. However, I could not find this configuration in /etc/trove/trove-guestagent.conf. It toke me much time to figure it out and find the clue from the source code.

Please add all alternative configurations in the default configuration files. It helps and saves us time.