minijail0: adjust how we stop processing non-opts

Commit f65c9fed1a54659d309775b5eeee6800569b0547 ([minijail] stop parsing
at first non-opt arg) worked by hand checking each argument itself to see
if it started with a dash.  The initial shortcircuit logic though ends up
breaking default init code that is at the end of parse_args like how we
default to forwarding signals.

Let's delete the hand parsing logic and let getopt do this for us.  It has
a mode already when the optstring starts with a "+".

BUG=chromium:730682
TEST=`./minijail0 ./a.out` forwards signals
TEST=`./minijail0 -z /bin/ls --help` triggers ls's help output

Change-Id: I949e29669bb09f9cced03f911ade0505c84e542d
1 file changed