test: test_rebind.py doesn't use a temporary a DataDirectory

Riastradh on IRC reported this with test_rebind.sh:

Tor logged: "Nov 21 20:08:11.296 [warn] Error creating directory /home/riastradh/.tor:

That test is not using a temporary dir (example: mktemp -d) so tor is using the default one which is ~/.tor.

Really not good, out tests should not poke $HOME whatsoever unless we change it. Solution would be to create a temp dir, spawn Tor pointing it to that path and then remove it.