Parsing pool default query options should ignore invalid opts

In 2.5 we added the ability to set per-pool default query options. A string of key-value pairs can be specified with a pool configuration. However, if any options fail to parse, then all the options are ignored. We want that behavior (and returning an error) when parsing the process-wide default query options on startup and when parsing the options sent from a client (e.g. in beeswax server) because an error can be returned immediately for the triggering action at that time (i.e. starting the impalad or submitting a query with the options set). However, in this case, the administrator is likely the one who set these default query options and it may have been set earlier in the pool configuration. It would be best to allow other valid query options to go through.