Django GPG: 3rd party app compatibility update

Update the django_gpg app to work with the latest version of the
python-gnupg package (0.4.3).

The python-gnupg now returns a more clear error message to
differentiate between a bad passphrase and a missing passphrase.
This improments allows the django_gpg to simplify its error
message parsing and remove the literals:
"ERROR_MSG_NEED_PASSPHRASE" and "ERROR_MSG_GOOD_PASSPHRASE".

Signed-off-by: Roberto Rosario <Roberto.Rosario@mayan-edms.com>

mayan/apps/django_gpg/models.py

@@ -11,9 +11,8 @@ from django.utils.translation import ugettext_lazy as _
 
 from .exceptions import NeedPassphrase, PassphraseError
 from .literals import (
-    ERROR_MSG_NEED_PASSPHRASE, ERROR_MSG_BAD_PASSPHRASE,
-    ERROR_MSG_GOOD_PASSPHRASE, KEY_TYPE_CHOICES, KEY_TYPE_SECRET,
-    OUTPUT_MESSAGE_CONTAINS_PRIVATE_KEY
+    ERROR_MSG_BAD_PASSPHRASE, ERROR_MSG_MISSING_PASSPHRASE,
+    KEY_TYPE_CHOICES, KEY_TYPE_SECRET, OUTPUT_MESSAGE_CONTAINS_PRIVATE_KEY
 )
 from .managers import KeyManager
 from .runtime import gpg_backend
@@ -124,10 +123,10 @@ class Key(models.Model):
 
         logger.debug('file_sign_results.stderr: %s', file_sign_results.stderr)
 
-        if ERROR_MSG_NEED_PASSPHRASE in file_sign_results.stderr:
-            if ERROR_MSG_BAD_PASSPHRASE in file_sign_results.stderr:
-                raise PassphraseError
-            elif ERROR_MSG_GOOD_PASSPHRASE not in file_sign_results.stderr:
-                raise NeedPassphrase
+        if ERROR_MSG_MISSING_PASSPHRASE in file_sign_results.stderr:
+            raise NeedPassphrase
+
+        if ERROR_MSG_BAD_PASSPHRASE in file_sign_results.stderr:
+            raise PassphraseError
 
         return file_sign_results