put user and url list creation in the unittest on the module level

move get_url_list and get_user_list out of the
TestHttpApi (renamed from TestHttpStorageApi) class
to the module level so that they can be used by other
test classes.
fix private function names in irodsstorage

private modules functions should have only
one _ instead of two.
(__ is for private class methods)
update file and folder definitions in mockstorage
add test for the storage API; add file definitions

add a new class with tests against the storage API.
This complements the http tests.
- httptests runs with a fully mocked storage and expect
    a well-implemented storage interface to test cdmi.py
- the storagetests test if the storages implement the
    API correctly.
    The aim is to detach the storages from the backend
    so that we can mock the backend functions, but it's
    not clear if that's possible.

    Either way the tests should run without further mockin
    as functional tests. Mocking is only to enable them to
    be run as automated unit tests.