lxc-autostart: rework boot and group handling

This adds new functionality to lxc-autostart.

*) The -g / --groups option is multiple cummulative entry.
	This may be mixed freely with the previous comma separated
	group list convention.  Groups are processed in the
	order they first appear in the aggregated group list.

*) The NULL group may be specified in the group list using either a
	leading comma, a trailing comma, or an embedded comma.

*) Booting proceeds in order of the groups specified on the command line
	then ordered by lxc.start.order and name collalating sequence.

*) Default host bootup is now specified as "-g onboot," meaning that first
	the "onboot" group is booted and then any remaining enabled
	containers in the NULL group are booted.

*) Adds documentation to lxc-autostart for -g processing order and
	combinations.

*) Parameterizes bootgroups, options, and shutdown delay in init scripts
	and services.

*) Update the various init scripts to use lxc-autostart in a similar way.

Reported-by: CDR <venefax@gmail.com>
Signed-off-by: Dwight Engen <dwight.engen@oracle.com>
Signed-off-by: Michael H. Warfield <mhw@WittsEnd.com>
Acked-by: Stéphane Graber <stgraber@ubuntu.com>