Fix filenames in sharing integration tests

When a file is shared and the receiver of the share already has a file
with the same name that file is left untouched, and "(2)" is appended to
the name of the shared file.

As "textfile0.txt" is included in the user folder skeleton all the users
in the integration test have that file, so when it is shared the
receiver sees the share as "/textfile0 (2).txt", and her own file as
"/textfile0.txt".

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