Merge pull request #133 from edx/e0d/migrate-as-other-user

Adding a new env to handle escalating privileges to run db migrations.

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 
+LMS with enough privileges to modify the database schema.
+"""
+
+# Import everything from .aws so that our settings are based on those.
+from .aws import *
+import os
+
+USER = os.environ.get('DB_MIGRATION_USER', 'root')
+PASSWORD = os.environ.get('DB_MIGRATION_PASS', None)
+
+if not PASSWORD:
+   raise ImproperlyConfigured("No database password was provided for running "
+                              "migrations.  This is fatal.")
+
+DATABASES['default']['USER'] = USER
+DATABASES['default']['PASSWORD'] = PASSWORD