Fix issue with process invocation when using dash

Debian and ubuntu use `dash` as their system shell (/bin/sh). When dash is sent a SIGTERM, it does not kill the children processes. When foreman launches a command, it has the shell running as it's child, and then the actual command running as a child of the shell. When foreman sends a SIGTERM, it only kills the shell, and the children of the shell remain running.