Hello Stratis developers!

I attempted to run the `make test-real` on a virtual machine of Fedora 26-1.5 Server. One of the tests failed, and I'm wondering if that is important enough to post as an issue.

To be more specific, when I try to run `real_test_empty_pool,` it fails at one of the `unwrap()`s:
make test-real
sudo env "PATH=/usr/local/bin:/usr/bin:/usr/local/sbin:/usr/sbin:/home/jsalzberg/.cargo/bin:/home/jsalzberg/Programming/stratisd/target/debug:/home/jsalzberg/.local/bin:/home/jsalzberg/bin" RUSTFLAGS='-D warnings' RUST_BACKTRACE=1 cargo test -- --test real_test_empty_pool
   Compiling libstratis v0.1.1 (file:///home/jsalzberg/Programming/stratisd)
    Finished dev [unoptimized + debuginfo] target(s) in 4.55 secs
     Running target/debug/deps/libstratis-a40f09f70f597433

running 0 tests

test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 56 filtered out

     Running target/debug/deps/stratisd-29c4deddc9023466

running 0 tests

test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out

     Running target/debug/deps/loopbacked_tests-3d242529a0f13830

running 0 tests

test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 17 filtered out

     Running target/debug/deps/real_tests-aea58de6898d93b0

running 1 test
test real_test_empty_pool ... FAILED

failures:

---- real_test_empty_pool stdout ----
    thread 'real_test_empty_pool' panicked at 'called `Result::unwrap()` on an `Err` value: Error { repr: Os { code: 2, message: "No such file or directory" } }', src/libcore/result.rs:860:4
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
stack backtrace:
   0: std::sys::imp::backtrace::tracing::imp::unwind_backtrace
   1: std::sys_common::backtrace::_print
   2: std::panicking::default_hook::{{closure}}
   3: std::panicking::default_hook
   4: std::panicking::rust_panic_with_hook
   5: std::panicking::begin_panic_new
   6: std::panicking::begin_panic_fmt
   7: rust_begin_unwind
   8: core::panicking::panic_fmt
   9: core::result::unwrap_failed
             at /builddir/build/BUILD/rustc-1.20.0-src/src/libcore/macros.rs:41
  10: <core::result::Result<T, E>>::unwrap
             at /builddir/build/BUILD/rustc-1.20.0-src/src/libcore/result.rs:738
  11: real_tests::test_with_spec
             at tests/real_tests.rs:116
  12: real_tests::real_test_empty_pool
             at tests/real_tests.rs:196
  13: <F as test::FnBox<T>>::call_box
  14: __rust_maybe_catch_panic


failures:
    real_test_empty_pool

test result: FAILED. 0 passed; 1 failed; 0 ignored; 0 measured; 16 filtered out

PS: That test is written with a lot of `unwrap()`s, and it is hard to tell which of the `unwrap()`s causes the error. Should they all be changed to `expect("")`s?