fix(confd): services check for valid config before reloading

Adds a check_cmd to controller, database, and registry that will prevent their processes from reloading if configuration files are invalid. This is already in place for deis-router, logger does not use confd templating, and builder does not have a process that needs reloading. (Cache runs Redis in the foreground, and Redis ignores SIGHUP completely, so it's problematic.)

TESTING: Build controller, database, and registry. Test that `make uninstall` and `make run` work and that stopping and starting individual components does not cause others to fail with invalid configuration.