Better feed back for missing intent/entity files

mycroft/skills/core.py

@@ -155,6 +155,10 @@ def load_skill(skill_descriptor, bus, skill_id, BLACKLISTED_SKILLS=None):
             return skill
         else:
             LOG.warning("Module {} does not appear to be skill".format(name))
+    except FileNotFoundError as e:
+        LOG.error(
+            'Failed to load {} due to a missing file: {}'.format(name, str(e))
+            )
     except Exception:
         LOG.exception("Failed to load skill: " + name)
     return None
@@ -989,7 +993,9 @@ class MycroftSkill:
 
         filename = self.find_resource(intent_file, 'vocab')
         if not filename:
-            raise ValueError('Unable to find "' + str(intent_file) + '"')
+            raise FileNotFoundError(
+                'Unable to find "' + str(intent_file) + '"'
+                )
 
         data = {
             "file_name": filename,
@@ -1021,7 +1027,9 @@ class MycroftSkill:
 
         filename = self.find_resource(entity_file + ".entity", 'vocab')
         if not filename:
-            raise ValueError('Unable to find "' + entity_file + '.entity"')
+            raise FileNotFoundError(
+                'Unable to find "' + entity_file + '.entity"'
+                )
         name = str(self.skill_id) + ':' + entity_file
 
         self.bus.emit(Message("padatious:register_entity", {