AMBARI-3180. Helper script for HDP upgrade (improve error message).

ambari-server/pom.xml

@@ -348,6 +348,9 @@
                 <source>
                   <location>src/main/resources/scripts/distribute_keytabs.py</location>
                 </source>
+                <source>
+                  <location>src/main/python/UpgradeHelper_HDP2.py</location>
+                </source>
               </sources>
             </mapping>
             <mapping>

ambari-server/src/main/python/UpgradeHelper_HDP2.py

@@ -338,8 +338,9 @@ def read_mapping():
   if os.path.isfile(MR_MAPPING_FILE):
     return json.load(open(MR_MAPPING_FILE))
   else:
-    raise FatalException(-1, "MAPREDUCE host mapping file is not available or badly formatted. Execute action "
-                             "save-mr-mapping or manually create the file.")
+    raise FatalException(-1, "MAPREDUCE host mapping file, mr_mapping, is not available or badly formatted. Execute "
+                             "action save-mr-mapping. Ensure the file is present in the directory where you are "
+                             "executing this command.")
   pass