`/usr/bin/yes` could produce output very quickly (100s of MBps on my
laptop) and therefore could cause log files to roll over.
A bash loop with a sleep avoids that issue. The test is slower but
should be much more resilient to the massive timing differences between
workstations and Travis.
- Properly expects the hard-coded mounts (alloc, dev, and proc) and hardcoded local directories (local and tmp)
- Also verifies that etc contains only the requested paths
- Simplify map length check in Linux Executor
- Added a `chroot_env` test for config parser
- Moved `ChrootEnv` field from ExecutorCommand to ExecutorContext
- Added a test for `chroot_env` functionality
