Use name instead of label for the nesting stack

[tobiash]

I'm not entirely sure on this one, but since the inheritFrom field is supposed to contain a name, the nesting stack should also contain name instead of label.
I was not able to run all tests, but this fixes my problems with nesting podTemplate on my Jenkins instance.

[carlossg]

what's the problem and how does it manifest?

[tobiash]

Without this change, nesting podTemplate does not work at all for me in 0.11. It just uses the configuration from the innermost podTemplate. I think this is because #133 changed the code to lookup parent templates by name rather than by label.

[iocanel]

@tobiash: you are right!

#133 was incomplete and your change is required.