blank lines removed
remove unused import
test init_cache()

There is an error in init_cache from refactoring. 'self' isn't defined in this
scope since it is a class method. The test does not show this however, because
the generic Exception -- in this case also the NameError -- is silently (more
or less) discarded.
flake8 the sources to detect undefined names

Currently:

[WARN]  flake8: src/main/python/yadtbroadcastserver/__init__.py:115:22: F821
undefined name 'self'
[WARN]  flake8: src/main/python/yadtbroadcastserver/__init__.py:123:22: F821
undefined name 'self'
[WARN]  flake8 found 2 warning(s).
use a setUp in TestCache
expose broken refactor, self not defined
fix code, but test still broken

The temporary workaround for this is to make cache_file a class method instead
of an instance property. The test still fails, because the import of the config
failes.
proper test with mock for store_cache