Make local_storage_path configurable.

Heroku and other systems don't support writing to /tmp.
So the local_storage_path property should be exposable.

See https://github.com/grangier/python-goose/issues/61
Merge branch 'local_storage_path' of https://github.com/adamlwgriffiths/python-goose into adamlwgriffiths-local_storage_path
#86 - pep8
#86 - add tests
Merge branch 'feature/local-storage-path-86' into develop