test/zdtm.py: ignore UNIX sockets during report creation

When files are added to the report shutil.copytree is unhappy with
lazy-pages.socket. Tell shutil.copytree that it should ignore *.socket.

Signed-off-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>