gnu: duplicity: Fix and disable some tests.

* gnu/packages/patches/duplicity-piped-password.patch: New patch.
* gnu/packages/patches/duplicity-test_selection-tmp.patch: New patch.
* gnu-system.am (dist_patch_DATA): Add them.
* gnu/packages/backup.scm (duplicity)[source]: Add patches field.
  [inputs]: Add util-linux and tzdata.
  [arguments]: rename patch-tests phase to check-setup.  Set HOME and TZDIR
  for tests.