keyinfo should always contain project attribute

[dmach]

Issue Description

/source/<project>/_keyinfo should not return empty <keyinfo/>.
It should contain the project attribute: <keyinfo project="<project>"/>.

This happens when the output contains no keys.
If there are keys, the attribute is present.

[adrianschroeter]

there are cases where the key is defined external. So there is no valid project name which defines the key. For example when the instance key is used as fallback.

I think you need to live with the situation that it is not always set.