debug: disable daemon and closeallfds

Support options for debugging in erlxc_drv:

    erlxc_drv:start("test", [nodaemonize,nocloseallfds])

nodaemonize: calling liblxc:start/3 will block until the container
exits. liblxc error messages are printed to stderr.

nocloseallfds: when running in daemon mode, liblxc by default closes all
open file descriptors. This will cause problems when running under
valgrind (valgrind reserves the 10 top fd's for its use).
erlxc: clean up usage