Rename env var for AWS_SHARED_CREDENTIALS_FILE

Note that this is just changing a config value.
Also added an integration test for this.

botocore/session.py

@@ -82,7 +82,8 @@ class Session(object):
         # These variables are intended for internal use so don't have any
         # user settable values.
         # This is the shared credentials file amongst sdks.
-        'credentials_file': (None, 'AWS_CREDENTIALS_FILE', '~/.aws/credentials', None),
+        'credentials_file': (None, 'AWS_SHARED_CREDENTIALS_FILE',
+                             '~/.aws/credentials', None),
 
         # These variables only exist in the config file.
 

tests/integration/test_credentials.py

@@ -15,7 +15,7 @@
 import mock
 
 from botocore.session import Session
-from tests import BaseEnvVar
+from tests import BaseEnvVar, temporary_file
 
 
 class TestCredentialPrecedence(BaseEnvVar):
@@ -107,3 +107,16 @@ def test_access_secret_env_vs_profile_code(self):
 
         self.assertEqual(credentials.access_key, 'test')
         self.assertEqual(credentials.secret_key, 'test-secret')
+
+    def test_honors_aws_shared_credentials_file_env_var(self):
+        with temporary_file('w') as f:
+            f.write('[default]\n'
+                    'aws_access_key_id=custom1\n'
+                    'aws_secret_access_key=custom2\n')
+            f.flush()
+            os.environ['AWS_SHARED_CREDENTIALS_FILE'] = f.name
+            s = Session()
+            credentials = s.get_credentials()
+
+            self.assertEqual(credentials.access_key, 'custom1')
+            self.assertEqual(credentials.secret_key, 'custom2')