add fake authentication to localstorage

to let the unit tests pass. the usernames and password
are given through the config.py.
if none are, everyone can access -- this helps the dev use case
fix and update mockstorage
update unittests for test with multiple backends

add functionality to modify the tested urls
(read: files and folders)

local storage has a /tmp/new prefix, so that it's all writable
and we can predict the metadata (e.g. #children)

irods will have /tempZone/home/eirods prefixed, but its'
not done yet.
fix stat error code on localstorage
fix HttpApi unittests: use shutil.rmtree for deleting things
fix HttpApi unittest: delete function now supports files and dirs
fix localstorage remove functions

1. fix error handling with a utility function for errnos
2. fix the rm function to also handle dir deletion
    by raising an IsDirException
test the local backend in travis unittests

mock does not pass all of them anymore, and I will
probably discontinue it ...