Your kernel does not appear to be compiled with support for unprivileged user
namespaces (CONFIG_USER_NS=y), or something else is preventing creation of user
namespaces. This feature is critical for sandboxing. Arch Linux is known to
ship with a kernel that disables this feature; if you are using Arch, you will
unfortunately need to compile your own kernel (see
https://bugs.archlinux.org/task/36969). If you are not using Arch, and don't
know why your system wouldn't have user namespaces, please file a bug against
Sandstorm so we can figure out what happened.
*** INSTALLATION FAILED ***
Report bugs at: http://github.com/sandstorm-io/sandst