Added hostIdentifier to info output

Small change that adds the the hostIdentifier in the output to the info log when running queries.

Also, wraps the `DBHandle::getInstance()` call in a try block, an cause the `getHostIdentifier()` function to throw an error if it cant access the DB.
Looks like it is still there...are you planning on removing it soon?
https://github.com/facebook/osquery/blob/master/osquery/scheduler/scheduler.cpp#L65