lxc: Better handle arguments
lxc: Better handle arguments

This allows things like:

 - lxc --project=blah shell abc
 - lxc --debug shell abc

Not that it aliases cannot support leading flags with value separated by
spaces as the alias handling logic does not know what flag is a boolean
and what flag takes a value.

As a result, use `lxc --project=blah shell` and not `lxc --project blah shell`
as the latter cannot work and will lead to a confusing error.

Closes #7625

Signed-off-by: Stéphane Graber <089afc6d81f66f1168a9849e15660feae286e024@ubuntu.com>

stgraber/lxd,hallyn/lxd,lxc/lxd,hallyn/lxd,atxwebs/lxd,hallyn/lxd,atxwebs/lxd,stgraber/lxd,hallyn/lxd,hallyn/lxd,atxwebs/lxd,stgraber/lxd,lxc/lxd,stgraber/lxd,stgraber/lxd,lxc/lxd,lxc/lxd,lxc/lxd,hallyn/lxd,stgraber/lxd,stgraber/lxd,lxc/lxd,atxwebs/lxd,lxc/lxd