adding db overrides to aws_migrate.py

lms/envs/aws_migrate.py

 """
-A Django settings file for use on AWS while running 
-database migrations, since we don't want to normally run the 
+A Django settings file for use on AWS while running
+database migrations, since we don't want to normally run the
 LMS with enough privileges to modify the database schema.
 """
 
@@ -13,12 +13,17 @@ from .aws import *
 import os
 from django.core.exceptions import ImproperlyConfigured
 
-USER = os.environ.get('DB_MIGRATION_USER', 'root')
-PASSWORD = os.environ.get('DB_MIGRATION_PASS', None)
+DB_OVERRIDES = dict(
+    USER=os.environ.get('DB_MIGRATION_USER', 'root'),
+    PASSWORD=os.environ.get('DB_MIGRATION_PASS', None),
+    NAME=os.environ.get('DB_MIGRATION_NAME', DATABASES['default']['NAME']),
+    HOST=os.environ.get('DB_MIGRATION_HOST', DATABASES['default']['HOST']),
+    PORT=os.environ.get('DB_MIGRATION_PORT', DATABASES['default']['PORT']),
+)
 
-if not PASSWORD:
-   raise ImproperlyConfigured("No database password was provided for running "
-                              "migrations.  This is fatal.")
+if not DB_OVERRIDES['PASSWORD']:
+    raise ImproperlyConfigured("No database password was provided for running "
+                               "migrations.  This is fatal.")
 
-DATABASES['default']['USER'] = USER
-DATABASES['default']['PASSWORD'] = PASSWORD
+for override, value in DB_OVERRIDES.iteritems():
+    DATABASES['default'][override] = value