fix: Be able to connect to SQL in containers.

By default if you use `localhost` as the `HOST` value for mysql, it
tries to connect to a file socket on disk rather than trying to connect
to the loopback hostname.  This prevents us from running MySQL in a
container while running the LMS on your local machine.

Setting the host to `127.0.0.1` forces the SQL connection to go over TCP
instead. This allows you to map your container port to your localhost
without any issues.

lms/envs/common.py

@@ -1640,7 +1640,7 @@ DATABASES = {
         'ATOMIC_REQUESTS': True,
         'CONN_MAX_AGE': 0,
         'ENGINE': 'django.db.backends.mysql',
-        'HOST': 'localhost',
+        'HOST': '127.0.0.1',
         'NAME': 'edxapp',
         'OPTIONS': {},
         'PASSWORD': 'password',
@@ -1650,7 +1650,7 @@ DATABASES = {
     'read_replica': {
         'CONN_MAX_AGE': 0,
         'ENGINE': 'django.db.backends.mysql',
-        'HOST': 'localhost',
+        'HOST': '127.0.0.1',
         'NAME': 'edxapp',
         'OPTIONS': {},
         'PASSWORD': 'password',
@@ -1660,7 +1660,7 @@ DATABASES = {
     'student_module_history': {
         'CONN_MAX_AGE': 0,
         'ENGINE': 'django.db.backends.mysql',
-        'HOST': 'localhost',
+        'HOST': '127.0.0.1',
         'NAME': 'edxapp_csmh',
         'OPTIONS': {},
         'PASSWORD': 'password',