Linux TravisCI failure on master

[jdm]

     Running `/home/travis/build/servo/gaol/target/debug/deps/file_read_all-4db1d97cb18b5209`
thread 'main' panicked at 'assertion failed: unshare(CLONE_NEWUSER | CLONE_NEWPID) == 0', platform/linux/namespace.rs:193:4
note: Run with `RUST_BACKTRACE=1` for a backtrace.
thread 'main' panicked at 'assertion failed: libc::read(pipe_fds[0], &mut grandchild_pid as *mut i32 as *mut c_void,
           mem::size_of::<pid_t>() as size_t) ==
    mem::size_of::<pid_t>() as ssize_t', platform/linux/namespace.rs:271:8
note: Run with `RUST_BACKTRACE=1` for a backtrace.
error: test failed, to rerun pass '--test file-read-all'

[jdm]

@pcwalton Any chance you could take a look at this?

[pcwalton]

Can you give me more info on (or let me know how to find) the exact Linux distro and version that this builder is using? I think it may be that namespaces are disabled in that Linux config or something like that.

[jdm]

@pcwalton The TravisCI job says:

Distributor ID: Ubuntu
Description:    Ubuntu 14.04.5 LTS
Release:    14.04
Codename:   trusty
Runtime kernel version: 4.14.12-041412-generic

That's from the "Build system information" dropdown in https://travis-ci.org/servo/gaol/jobs/358137831.

[pcwalton]

Aha, 4 years old. That's suspicious. I'll download that image and try to reproduce in a VM.

[pcwalton]

I'm having trouble reproducing this on that version of Ubuntu, unfortunately…

[Eijebong]

Fixed by #50