now missing hosts file gives nice message and no traceback

Signed-off-by: Brian Coca <briancoca+dev@gmail.com>

lib/ansible/inventory/__init__.py

@@ -80,7 +80,8 @@ class Inventory(object):
                     all.add_host(Host(tokens[0], tokens[1]))
                 else:
                     all.add_host(Host(x))
-        elif utils.is_executable(host_list):
+        elif os.path.exists(host_list):
+            if utils.is_executable(host_list):
                 self._is_script = True
                 self.parser = InventoryScript(filename=host_list)
                 self.groups = self.parser.groups.values()
@@ -91,6 +92,8 @@ class Inventory(object):
                     self.groups = self.parser.groups.values()
                 else:
                     raise errors.AnsibleError("YAML inventory support is deprecated in 0.6 and removed in 0.7, see the migration script in examples/scripts in the git checkout")
+        else:
+            raise errors.AnsibleError("No valid hosts inventory file found")
 
     def _match(self, str, pattern_str):
         if pattern_str.startswith('~'):