Jwst.Edb.GetTimeseries service request no longer works

The service request to retrieve mnemonic information from the JWST engineering database no longer works. Using `astroquery 0.4` I get the following error:

```
from astroquery.mast import Mast
service = "Mast.JwstEdb.GetTimeseries.All"
params = {'mnemonic': 'SA_ZADUCMDX',
'start':'2019-05-31 23:59:58',
'end':'2019-06-01 23:59:59'}

out = Mast.service_request(service, params, fetch_name="Mast.JwstEdb", pagesize=1000)

---------------------------------------------------------------------------
RemoteServiceError Traceback (most recent call last)
in
----> 1 out = Mast.service_request(service, params, fetch_name="Mast.JwstEdb", pagesize=1000)

~/anaconda3/lib/python3.7/site-packages/astroquery/utils/class_or_instance.py in f(*args, **kwds)
23 def f(*args, **kwds):
24 if obj is not None:
---> 25 return self.fn(obj, *args, **kwds)
26 else:
27 return self.fn(cls, *args, **kwds)

~/anaconda3/lib/python3.7/site-packages/astroquery/utils/process_asyncs.py in newmethod(self, *args, **kwargs)
27 if kwargs.get('get_query_payload') or kwargs.get('field_help'):
28 return response
---> 29 result = self._parse_result(response, verbose=verbose)
30 self.table = result
31 return result

~/anaconda3/lib/python3.7/site-packages/astroquery/mast/core.py in _parse_result(self, responses, verbose)
605 # check for error message
606 if result['status'] == "ERROR":
--> 607 raise RemoteServiceError(result.get('msg', "There was an error with your request."))
608
609 result_table = _mashup_json_to_table(result, col_config)

RemoteServiceError: Object reference not set to an instance of an `object.`
```

After updating to `0.4.1` I get a different error:
```
out = Mast.service_request(service, params, fetch_name="Mast.JwstEdb", pagesize=1000)

---------------------------------------------------------------------------
NameError Traceback (most recent call last)
in
----> 1 out = Mast.service_request(service, params, fetch_name="Mast.JwstEdb", pagesize=1000)

~/anaconda3/lib/python3.7/site-packages/astroquery/utils/class_or_instance.py in f(*args, **kwds)
23 def f(*args, **kwds):
24 if obj is not None:
---> 25 return self.fn(obj, *args, **kwds)
26 else:
27 return self.fn(cls, *args, **kwds)

~/anaconda3/lib/python3.7/site-packages/astroquery/utils/process_asyncs.py in newmethod(self, *args, **kwargs)
27 if kwargs.get('get_query_payload') or kwargs.get('field_help'):
28 return response
---> 29 result = self._parse_result(response, verbose=verbose)
30 self.table = result
31 return result

~/anaconda3/lib/python3.7/site-packages/astroquery/mast/observations.py in _parse_result(self, responses, verbose)
796 """
797
--> 798 return self._portal_api_connection._parse_result(responses, verbose)
799
800 @class_or_instance

~/anaconda3/lib/python3.7/site-packages/astroquery/mast/discovery_portal.py in _parse_result(self, responses, verbose)
289 # check for error message
290 if result['status'] == "ERROR":
--> 291 raise RemoteServiceError(result.get('msg', "There was an error with your request."))
292
293 result_table = _json_to_table(result, col_config)

NameError: name 'RemoteServiceError' is not defined
```

Reproduce the two Mast.service_request examples and inspect the parsing paths shown in astroquery/mast/core.py, observations.py, and discovery_portal.py. Check the JwstEdb service response and the missing RemoteServiceError handling; done means the reported request no longer fails with either shown error.

Written by the indexing model from the issue text.