Added checks to FrequencyUnit string parsing

Author: Nicholas King

src/ResourceManager/Websites/Commands.Websites/Cmdlets/BackupRestore/BackupRestoreUtils.cs

@@ -10,7 +10,14 @@ internal class BackupRestoreUtils
         public static FrequencyUnit StringToFrequencyUnit(string frequencyUnit)
         {
             FrequencyUnit freq;
-            Enum.TryParse(frequencyUnit, true, out freq);
+            try
+            {
+                freq = (FrequencyUnit) Enum.Parse(typeof (FrequencyUnit), frequencyUnit, true);
+            }
+            catch (ArgumentException)
+            {
+                throw new ArgumentException(string.Format("{0} is not a valid FrequencyUnit. Valid options are Hour and Day.", frequencyUnit));
+            }
             return freq;
         }