Use iso8601 to validate scheduled_for datetime.

Added a validation method that always fails for scheduled notifications.
Comment out config for scheduled task.
The schedule notifications will be turned on once we can invite services to use it.
Waiting for the service permission story, must commit this in order to keep things from going stale.

app/schema_validation/__init__.py

@@ -1,6 +1,7 @@
 import json
 from datetime import datetime, timedelta
 
+from iso8601 import iso8601, ParseError
 from jsonschema import (Draft4Validator, ValidationError, FormatChecker)
 from notifications_utils.recipients import (validate_phone_number, validate_email_address, InvalidPhoneError,
                                             InvalidEmailError)
@@ -25,14 +26,14 @@ def validate(json_to_validate, schema):
     def validate_schema_date_with_hour(instance):
         if isinstance(instance, str):
             try:
-                dt = datetime.strptime(instance, "%Y-%m-%d %H:%M")
+                dt = iso8601.parse_date(instance).replace(tzinfo=None)
                 if dt < datetime.utcnow():
                     raise ValidationError("datetime can not be in the past")
                 if dt > datetime.utcnow() + timedelta(hours=24):
                     raise ValidationError("datetime can only be 24 hours in the future")
-            except ValueError as e:
-                raise ValidationError("datetime format is invalid. Use the format: "
-                                      "YYYY-MM-DD HH:MI, for example 2017-05-30 13:15")
+            except ParseError:
+                raise ValidationError("datetime format is invalid. It must be a valid ISO8601 date time format, "
+                                      "https://en.wikipedia.org/wiki/ISO_8601")
         return True
 
     validator = Draft4Validator(schema, format_checker=format_checker)