Merge pull request #3890 from edx/derf/parameterize_cms_migrations

copied from LMS aws_migrate settings

cms/envs/aws_migrate.py

@@ -13,12 +13,18 @@ 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(
+    PASSWORD=os.environ.get('DB_MIGRATION_PASS', None),
+    ENGINE=os.environ.get('DB_MIGRATION_ENGINE', DATABASES['default']['ENGINE']),
+    USER=os.environ.get('DB_MIGRATION_USER', DATABASES['default']['USER']),
+    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:
+if DB_OVERRIDES['PASSWORD'] is None:
     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