Fix check for springBootApplication elements

[cherylking]

The check added recently for more than one springBootApplication element only considered a single server config file. The check needs to take into account all server config files (via include elements and configDropins). I suggest the code should collect a Map of springBootApplication by id and preserve the correct merge/replace behavior based on where the config resides. Once all the server config files have been processed, check if more than one configured springBootApplication location exists and throw the error at that point. We could even include the ids for the elements we found in the message.