Log connect failures in BalancedClickhouseDataSource

[chrisribble]

It is very difficult to debug connect failures while using BalancedClickhouseDataSource as the code swallows all connect exceptions.

This adds a log so that it's actually possible to figure out why connect is failing for one or more JDBC URLs. I wasn't totally sure what the ethos is in this project WRT how much to log, so I started at debug, but would be happy to increase the log level.

[chrisribble]

@zhicwu @alexey-milovidov @qoega would it be possible to get some feedback on this change?

Please let me know if you would like me to approach this differently.

[zhicwu]

Sorry for the late response @chrisribble. It shouldn't take this long for adding log for debugging ;) I believe you've already made the change at your end, di you find anything interesting?

Anyway, could you change merge target of this PR from master to develop so that I can merge?

[chrisribble]

Sorry for the late response @chrisribble. It shouldn't take this long for adding log for debugging ;) I believe you've already made the change at your end, di you find anything interesting?

Anyway, could you change merge target of this PR from master to develop so that I can merge?

@zhicwu

Yes, by adding the change, we were able to discover that we had an authentication problem (the exception stack trace included information indicating that the credentials were not correct).

I've updated the PR to target the develop branch