test_backtrace fails consistently

[davide125]

When running cargo test on master I get:

test test_backtrace ... FAILED

failures:

---- test_backtrace stdout ----
thread 'test_backtrace' panicked at 'Unexpected stderr, failed var.contains("stack backtrace")
└── var as str: Error: this is some context
Info: caused by root cause failure
   0: failure::backtrace::internal::InternalBacktrace::new
             at /home/dcavalca/.cargo/registry/src/github.com-1ecc6299db9ec823/failure-0.1.8/src/backtrace/internal.rs:46:44
   1: failure::backtrace::Backtrace::new
             at /home/dcavalca/.cargo/registry/src/github.com-1ecc6299db9ec823/failure-0.1.8/src/backtrace/mod.rs:121:35
   2: <failure::error::error_impl::ErrorImpl as core::convert::From<F>>::from
             at /home/dcavalca/.cargo/registry/src/github.com-1ecc6299db9ec823/failure-0.1.8/src/error/error_impl.rs:19:17
   3: <failure::error::Error as core::convert::From<F>>::from
             at /home/dcavalca/.cargo/registry/src/github.com-1ecc6299db9ec823/failure-0.1.8/src/error/mod.rs:36:18
   4: failure::error_message::err_msg
             at /home/dcavalca/.cargo/registry/src/github.com-1ecc6299db9ec823/failure-0.1.8/src/error_message.rs:12:5
   5: example::some_fn
             at examples/example.rs:20:21
   6: example::main
             at examples/example.rs:16:8
   7: core::ops::function::FnOnce::call_once
             at /builddir/build/BUILD/rustc-1.54.0-src/library/core/src/ops/function.rs:227:5
   8: std::sys_common::backtrace::__rust_begin_short_backtrace
             at /builddir/build/BUILD/rustc-1.54.0-src/library/std/src/sys_common/backtrace.rs:125:18
   9: std::rt::lang_start::{{closure}}
             at /builddir/build/BUILD/rustc-1.54.0-src/library/std/src/rt.rs:49:18
  10: std::rt::lang_start_internal
  11: std::rt::lang_start
             at /builddir/build/BUILD/rustc-1.54.0-src/library/std/src/rt.rs:48:5
  12: main
  13: __libc_start_main
  14: _start



command=`"/home/dcavalca/fedora-wip/resctl-demo/r2/exitfailure/target/debug/examples/example"`
code=1
stdout=```""```
stderr=```"Error: this is some context\nInfo: caused by root cause failure\n   0: failure::backtrace::internal::InternalBacktrace::new\n             at /home/dcavalca/.cargo/registry/src/github.com-1ecc6299db9ec823/failure-0.1.8/src/backtrace/internal.rs:46:44\n   1: failure::backtrace::Backtrace::new\n             at /home/dcavalca/.cargo/registry/src/github.com-1ecc6299db9ec823/failure-0.1.8/src/backtrace/mod.rs:121:35\n   2: <failure::error::error_impl::ErrorImpl as core::convert::From<F>>::from\n             at /home/dcavalca/.cargo/registry/src/github.com-1ecc6299db9ec823/failure-0.1.8/src/error/error_impl.rs:19:17\n   3: <failure::error::Error as core::convert::From<F>>::from\n             at /home/dcavalca/.cargo/registry/src/github.com-1ecc6299db9ec823/failure-0.1.8/src/error/mod.rs:36:18\n   4: failure::error_message::err_msg\n             at /home/dcavalca/.cargo/registry/src/github.com-1ecc6299db9ec823/failure-0.1.8/src/error_message.rs:12:5\n   5: example::some_fn\n             at examples/example.rs:20:21\n   6: example::main\n             at examples/example.rs:16:8\n   7: core::ops::function::FnOnce::call_once\n             at /builddir/build/BUILD/rustc-1.54.0-src/library/core/src/ops/function.rs:227:5\n   8: std::sys_common::backtrace::__rust_begin_short_backtrace\n             at /builddir/build/BUILD/rustc-1.54.0-src/library/std/src/sys_common/backtrace.rs:125:18\n   9: std::rt::lang_start::{{closure}}\n             at /builddir/build/BUILD/rustc-1.54.0-src/library/std/src/rt.rs:49:18\n  10: std::rt::lang_start_internal\n  11: std::rt::lang_start\n             at /builddir/build/BUILD/rustc-1.54.0-src/library/std/src/rt.rs:48:5\n  12: main\n  13: __libc_start_main\n  14: _start\n\n"```
', /home/dcavalca/.cargo/registry/src/github.com-1ecc6299db9ec823/assert_cmd-1.0.8/src/assert.rs:124:9
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace


failures:
    test_backtrace

test result: FAILED. 4 passed; 1 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.07s