Many tests fail on system with non-executable /tmp

[nchaimov]

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On a system with /tmp mounted noexec, any test that involves compiling and running one of the example codes will fail. We should detect such a system and choose an alternate location to use in push_test_workdir().

[nchaimov]

paratools04 has /tmp/ mounted noexec, so this can be tested there. Tests will normally fail. They will succeed with, for example, export TMPDIR=/dev/shm