pkg-map: respect --missing-ok also on missing pkg-map file

When there is no pkg-map file for the specified element, list the passed
packages if --missing-ok is specified.

This mirrors what is being done already later, when a pkg-map file
exists but it does not have the mapping for the requested package.

Change-Id: I50287f8e6a5e4335deb3de2252075b8bfdd53ce5

elements/pkg-map/bin/pkg-map

@@ -64,6 +64,10 @@ def main():
     map_file = '/usr/share/pkg-map/%s' % args.element
     if not os.path.exists(map_file):
         eprint('Map file for %s element does not exist.' % args.element)
+        if args.missing_ok:
+            for name in extra:
+                print(name)
+            sys.exit(0)
         sys.exit(2)
 
     with open(map_file) as fd: