Default values are being overwritten by undefined prop values if state of parent component is updated [metal-jsx]

[kienD]

This issue is related to #259 .

The default value for props of a child component will be overwritten by the values passed in from the parent component once the state of the parent component changes. This is even if the value is undefined.

I would expect the default value for props of the child component to take precedence over an undefined value regardless of if it was on the first render or another render later on.

I sent pr for the broken test as well. #346