[bug] cache Executor waits for future to be evaluated

[jan-janssen]

While this functionality is necessary for subprocess based Executor the pysqa based Executor`can resolve dependencies on the queuing system level, so it is not required to wait on the python level. In general it might be reasonable to move the wait to the python process which is executing the python function, rather than waiting on the Exexutor level.

[jan-janssen]

The waiting happens in the execute_in_subprocess() function, which is fine as the subprocess interface is anyway primarily used for testing. Now that caching is available in the interactive jobs #435