Use standard logger for NewGitalyConnectivityCheck

Calling log.Configure() in multiple places leads to a data race because the same logger is getting its attributes set. This change uses the default logger.

fixes: #3902 (closed)

Note: in !4060 (merged), we will improve the usability of the check subcommmand by allowing users to pass in the -v flag to print out more verbose output. The logger is not really the right fit for this because human readable output is preferred for this subcommand.