walltime key missing from study run results in cryptic error message

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If walltime key is missing from the study run step, it should either fail the spec validation or indicate the key is missing.

2020-12-15 09:17:07,295 - maestrowf.datastructures.core.executiongraph:_execute_record:559 - INFO - Attempting submission of 'create_sdf' (attempt 1 of 1)...
2020-12-15 09:17:07,301 - maestrowf.conductor:main:387 - ERROR - ("time data '' does not match format '%H:%M:%S'",)
Traceback (most recent call last):
File "/g/g17/mast2/.local/lib/python3.6/site-packages/maestrowf-1.1.9.dev0-py3.6.egg/maestrowf/conductor.py", line 382, in main
completion_status = conductor.monitor_study()
File "/g/g17/mast2/.local/lib/python3.6/site-packages/maestrowf-1.1.9.dev0-py3.6.egg/maestrowf/conductor.py", line 352, in monitor_study
completion_status = dag.execute_ready_steps()
File "/g/g17/mast2/.local/lib/python3.6/site-packages/maestrowf-1.1.9.dev0-py3.6.egg/maestrowf/datastructures/core/executiongraph.py", line 870, in execute_ready_steps
self._execute_record(_record, adapter)
File "/g/g17/mast2/.local/lib/python3.6/site-packages/maestrowf-1.1.9.dev0-py3.6.egg/maestrowf/datastructures/core/executiongraph.py", line 565, in _execute_record
retcode = record.execute(adapter)
File "/g/g17/mast2/.local/lib/python3.6/site-packages/maestrowf-1.1.9.dev0-py3.6.egg/maestrowf/datastructures/core/executiongraph.py", line 95, in execute
retcode, jobid = self._execute(adapter, self.script)
File "/g/g17/mast2/.local/lib/python3.6/site-packages/maestrowf-1.1.9.dev0-py3.6.egg/maestrowf/datastructures/core/executiongraph.py", line 125, in _execute
self.step, script, self.workspace.value)
File "/g/g17/mast2/.local/lib/python3.6/site-packages/maestrowf-1.1.9.dev0-py3.6.egg/maestrowf/interfaces/script/fluxscriptadapter.py", line 650, in submit
job_name=step.name, force_broker=force_broker
File "/g/g17/mast2/.local/lib/python3.6/site-packages/maestrowf-1.1.9.dev0-py3.6.egg/maestrowf/interfaces/script/_flux/flux0_18_0.py", line 94, in submit
seconds = datetime.strptime(walltime, "%H:%M:%S")
File "/usr/mic/bio/anaconda3/lib/python3.6/_strptime.py", line 565, in _strptime_datetime
tt, fraction = _strptime(data_string, format)
File "/usr/mic/bio/anaconda3/lib/python3.6/_strptime.py", line 362, in _strptime
(data_string, format))
ValueError: time data '' does not match format '%H:%M:%S'

Read the walltime handling in maestrowf/interfaces/script/_flux/flux0_18_0.py, then trace how the step reaches submit through datastructures/core/executiongraph.py. Check the study specification validation path as well. Done means a missing walltime is rejected during validation or produces a clear missing-key error instead of the datetime parsing traceback.

Written by the indexing model from the issue text.