Do not fail when property does not exist

Fixes validation message during job import described in #1009 

Case:  'name' parameter missing in the job description 

Old behavior: import failed with error message displaying internal exception :
"groovy.lang.MissingPropertyException: No such property: adhocRemoteString for class:   rundeck.services.ScheduledExecutionService" 

New behavior: gracefully process missing properties and returns proper validation message: "Resource definition cannot contain null value.  Corresponding key: name"