singularity: bugfix add space between prefix and other options (#34766)

This fixes two issues introduced in #34474: prefix got the next
option appended, and property was not resolved without the self.

var/spack/repos/builtin/packages/singularityce/package.py

@@ -80,7 +80,7 @@ def config_options(self):
     def edit(self, spec, prefix):
         with working_dir(self.build_directory):
             confstring = "./mconfig --prefix=%s" % prefix
-            confstring += " ".join(config_options)
+            confstring += " " + " ".join(self.config_options)
             if "~suid" in spec:
                 confstring += " --without-suid"
             if "~network" in spec: