Allow 'cleanup' to run when no space is left

Be conservative and only unlock the 'cleanup' functionality, else we'd
have to check that all other actions handle ENOSPC gracefully.

Noticed at Concept Hygiene: https://assistance.tranquil.it/scp/tickets.php?id=2010

tisbackup.py

@@ -28,6 +28,7 @@ import sys
 import getopt
 import os.path
 import logging
+import errno
 from libtisbackup.common import *
 from libtisbackup.backup_mysql import backup_mysql
 from libtisbackup.backup_rsync import backup_rsync
@@ -369,9 +370,15 @@ def main():
 
     # if we run the nagios check, we don't create log file, everything is piped to stdout
     if action!='checknagios':
-        hdlr = logging.FileHandler(os.path.join(log_dir,'tisbackup_%s.log' % (backup_start_date)))
-        hdlr.setFormatter(logging.Formatter('%(asctime)s %(levelname)s %(message)s'))
-        logger.addHandler(hdlr)
+        try:
+            hdlr = logging.FileHandler(os.path.join(log_dir,'tisbackup_%s.log' % (backup_start_date)))
+            hdlr.setFormatter(logging.Formatter('%(asctime)s %(levelname)s %(message)s'))
+            logger.addHandler(hdlr)
+        except Exception, e:
+            if action == 'cleanup' and e.errno == errno.ENOSPC:
+                logger.warning("No space left on device, disabling file logging.")
+            else:
+                raise e
 
     # Main
     backup = tis_backup(dry_run=dry_run,verbose=verbose,backup_base_dir=backup_base_dir)