If we race with the logging thread and get to __wt_logmgr_destroy()
while __log_archive_once() is still using conn->log_path, we can free
it out from under the running server. If there's a logging thread
running, don't free conn->log_path until we've joined that thread.
Reference #1480.
whitespace
We don't need to store double quotes as the default value for
strings, an empty value is sufficient.