Fix several bugs related to sync errors, update some log messages

Fix several bugs related to sync errors, update some log messages

+Fix bug: an endless loop when a requested URI error was removed.
+Fix bug: some error'd URIs could be logged despite that their repository data was successfully fetched with another access method.
+Fig bug: if a TAL has more than one URI and there was an error fetching an URI, the following URIs in the list weren't considered to get the TA certificate.
+Only 'stderr' rsync output will be sent to operation log considering '--stale-repository-period', the 'stdout' rsync output will be sent to validation log at level info.
+Messages of rsync/rrdp retries are 'upgraded' from level info to warn (all on validation logs).
+Add a warning message (validation log) whenever local data is going to be utilized due to previous errors fetching repositories or TA certificates.
+Log all communication errors if 'log.level=debug'.