Fixed: Only log /proc/mounts exception once per process

Closes #3239

(cherry picked from commit ce0388ca99b7f89bd9e8971777a7995c4361d268)

src/NzbDrone.Mono/Disk/ProcMountProvider.cs

@@ -26,6 +26,7 @@ namespace NzbDrone.Mono.Disk
         private static Dictionary<string, bool> _fileSystems;
 
         private readonly Logger _logger;
+        private bool _hasLoggedProcMountFailure = false;
 
         public ProcMountProvider(Logger logger)
         {
@@ -45,7 +46,11 @@ namespace NzbDrone.Mono.Disk
             }
             catch (Exception ex)
             {
-                _logger.Debug(ex, "Failed to retrieve mounts from {0}", PROC_MOUNTS_FILENAME);
+                if (!_hasLoggedProcMountFailure)
+                {
+                    _logger.Debug(ex, "Failed to retrieve mounts from {0}", PROC_MOUNTS_FILENAME);
+                    _hasLoggedProcMountFailure = true;
+                }
             }
 
             return new List<IMount>();