bin: Better handle --

bin: Better handle --

We would stop passing through `--` and args after it to the underlying
command in `ostree_run`. This made it impossible to use `--` to tell the
parser that following args starting with `-` really are positional.

AFAICT, that logic for `--` here came from a time when we parse options
manually in a big loop, in which case breaking out made sense (see
97558276e4f855442337be01abc8f90cf0dd1810).

There's an extra step here, which is that glib by default leaves the
`--` in the list of args, so we need to take care to remove it from the
list after parsing.

Closes: #1898
Closes: #1899
Approved by: rfairley