Logger id (the one generated from build_id interface method and owner_id
property) is generated and cached the first time it is required, further
uses just return the cached value.
Add a cache reset method so if the interface implementer knows that its
logger id could have changed it could force its re-generation.
Signed-off-by: Maciej S. Szmigiero <mail@maciej.szmigiero.name>