Samuel Dionne-Riel 98419a0f64 nixos/tests/switch-test: Ensures the test fails on failure (#55744)
The `| tee` invocation always masked the return value of the
switch-to-configuration test.

```
~ $ false | tee && echo "oh no"
oh no
```

The added wrapper script will still output everything to stderr, while
passing failures to the test harness.
2019-02-14 22:55:16 +01:00
..

*** NixOS ***

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management system Nix.  More information can be found at
http://nixos.org/nixos and in the manual in doc/manual.