Grace period of >=24hours causes data corruption

[brianhempel]

A duration of "24:17:17" ends up being stored as "1 00:17:17" which can't be reparsed as a duration and breaks a number of subsequent CLI commands (include attempts to change the duration back to a valid value, but hitting the REST API directly is able to correct the problem).

$ chisubmit instructor assignment set-attribute lab07 grace_period 24:17:17
ERROR: Unexpected exception
Traceback (most recent call last):
  File "/usr/local/chisubmit_client/lib/python3.5/site-packages/chisubmit/client/types.py", line 128, in to_python
    return parse_timedelta(value)
  File "/usr/local/chisubmit_client/lib/python3.5/site-packages/chisubmit/common/utils.py", line 75, in parse_timedelta
    l = [int(x) for x in l]
  File "/usr/local/chisubmit_client/lib/python3.5/site-packages/chisubmit/common/utils.py", line 75, in <listcomp>
    l = [int(x) for x in l]
ValueError: invalid literal for int() with base 10: '1 00'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/local/chisubmit_client/lib/python3.5/site-packages/chisubmit/cli/common.py", line 93, in new_func
    return f(*args, **kwargs)
  File "/usr/local/chisubmit_client/lib/python3.5/site-packages/chisubmit/cli/common.py", line 62, in new_func
    return f(*args, **kwargs)
  File "/usr/local/chisubmit_client/lib/python3.5/site-packages/click/decorators.py", line 17, in new_func
    return f(get_current_context(), *args, **kwargs)
  File "/usr/local/chisubmit_client/lib/python3.5/site-packages/chisubmit/cli/common.py", line 83, in new_func
    return ctx.invoke(f, ctx.obj["course_obj"], *args, **kwargs)
  File "/usr/local/chisubmit_client/lib/python3.5/site-packages/click/core.py", line 555, in invoke
    return callback(*args, **kwargs)
  File "/usr/local/chisubmit_client/lib/python3.5/site-packages/click/decorators.py", line 17, in new_func
    return f(get_current_context(), *args, **kwargs)
  File "/usr/local/chisubmit_client/lib/python3.5/site-packages/chisubmit/cli/shared/assignment.py", line 46, in shared_assignment_set_attribute
    api_obj_set_attribute(ctx, assignment, attr_name, attr_value)
  File "/usr/local/chisubmit_client/lib/python3.5/site-packages/chisubmit/cli/common.py", line 281, in api_obj_set_attribute
    api_obj.edit(**{attr_name: v})
  File "/usr/local/chisubmit_client/lib/python3.5/site-packages/chisubmit/client/types.py", line 325, in edit
    self._updateAttributes(data)
  File "/usr/local/chisubmit_client/lib/python3.5/site-packages/chisubmit/client/types.py", line 254, in _updateAttributes
    checked_value = api_attr.to_python(attrvalue, self._headers, self._api_client)
  File "/usr/local/chisubmit_client/lib/python3.5/site-packages/chisubmit/client/types.py", line 184, in to_python
    return self.type.to_python(value, headers, api_client)
  File "/usr/local/chisubmit_client/lib/python3.5/site-packages/chisubmit/client/types.py", line 130, in to_python
    raise AttributeTypeException(value, self)
chisubmit.client.types.AttributeTypeException: ('1 00:17:17', <chisubmit.client.types.AttributeType object at 0x7f99b7e2e4e0>)