Clearer error message when SDK file cannot be found to stage

Change "directory" to "location" in error message when SDK file
cannot be found, now that --sdk_location can point to a tarball
as well as a directory.
----Release Notes----
[]
-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=117975068

Author: gildea

google/cloud/dataflow/utils/dependency.py

@@ -339,7 +339,7 @@ def stage_job_resources(options, file_copy=_dependency_file_copy,
                              sdk_path)
         else:
           raise RuntimeError(
-              'The file "%s" cannot be found. Its directory was specified by '
+              'The file "%s" cannot be found. Its location was specified by '
               'the --sdk_location command-line option.' %
               sdk_path)
 

google/cloud/dataflow/utils/dependency_test.py

@@ -260,7 +260,7 @@ def test_sdk_location_local_not_present(self):
       dependency.stage_job_resources(options)
     self.assertEqual(
         'The file "%s" cannot be found. Its '
-        'directory was specified by the --sdk_location command-line option.' %
+        'location was specified by the --sdk_location command-line option.' %
         sdk_location,
         cm.exception.message)