[swig-python] fix examples after e0c07d

KeySet.__getitem__ throws KeyError if key is missing
(see https://docs.python.org/3/reference/datamodel.html#object.__getitem__)

This fixes #1
swig-lua+python: fix installation directory
swig-lua: fix swig 3 compatibility
swig-python: another bug introducted by e0c07d
Get upstream changes.

Merge branch 'master' of github.com:ElektraInitiative/libelektra