allow registering extensions in installed system (bnc#876328)

(without re-registering the base product)

- removed BaseProduct - not needed anymore (the base product detection
  now works correctly)
- fixed connection initialization
Merge remote-tracking branch 'origin/master' into addons_in_registered_system

Conflicts:
	package/yast2-registration.changes
Merge pull request #74 from yast/addons_in_registered_system

Allow registering extensions in installed system (bnc#876328)