Conflicts:
	apps/files_encryption/lib/util.php
	apps/files_encryption/tests/hooks.php

The purpose of $originalStorage in unit tests was to remount the old
root.
However that storage itself is already wrapped by storage wrapper, so
remounting it would rewrap the storage several times.

This fix makes use of "loginAsUser()" and "logout()" from the TestCase
class to properly initialize and cleanup the FS as expected.

The check for invalid paths is actually over-complicated and performed twice resulting in a performance penalty. Additionally, I decided to add unit-tests to that function.

Part of https://github.com/owncloud/core/issues/13221

Now removing "/./" and trailing "/." from the paths when normalizing.

Legacy home storage ids with the format "local://path/to/datadir/user1"
are now also wrapped by the HomeStorage.

change behaviour of Filesystem::getMountPoint when a mountpoint is passed as path without trailing slash