QuantumEspressoRelax: apply options to base_final_scf namespace

[sphuber]

Fixes #219

The options from the engine dictionary passed to the get_builder
was only applied to the base namespace, but not to base_final_scf
which is what a user would expect.

[bosonie]

Just out of curiosity. If you do not specify any option, what resources are used? Do you have a default in CalcJob or in the BaseWorkChain. As far as I know native CalcJob requires computational resources.

[sphuber]

It currently sets the num_machines and a max_wallclock_seconds. However, this is actually problematic as this is scheduler dependent and, for example, when a computer with an SGE scheduler is used, it will fail, because num_machines are not supported there. I have described this problem in #174 and this applies to all generators. It is not obvious to me how to solve this though. There is no programmatic way (yet) to introspect a Scheduler implementation and determine the required attributes and a decent default. Important problem to tackle at some point though