Add integration tests for transferring ownership of reshares

Currently only transferring ownership of a reshare with a group to a
user in the group is possible.

When transferring ownership of a reshare with another user or with a
group to a user not in the group restoring the share fails (but the
command succeeds, it only fails for the specific files that are
reshares).

When transferring ownership of a path that is a reshare the command
fails (as when a specific path is provided the path tries to move the
file, it does not take into account reshares).

The added integration tests reflect the above behaviours.

Signed-off-by: Daniel Calviño Sánchez <danxuliu@gmail.com>