journal-upload: Update watchdog while in curl_easy_perform

journal-upload: Update watchdog while in curl_easy_perform

It is observed that a combination of high log throughput, low I/O speed on journal remote side and many nodes uploading simultaneously caused the journal-upload process to dump core because of watchdog starvation. This is caused because journal-upload stays in curl_easy_perform(), because it cannot upload fast enough to reach the end of the journal. Currently journal-upload will return from curl_easy_perform() only when the end of the journal is reached. Therefore a check is added in journal_input_callback(), which will update the watchdog if the elapsed time since the start of the uploading process is greater than WATCHDOG_USEC/2.