rb.postinstall(): don't allow configdir override

Since the templates need to match the contents of the configdir, it
doesn't really make sense to allow configdir to be different from
templatedir.

src/pylorax/__init__.py

@@ -197,7 +197,7 @@ class Lorax(BaseLoraxClass):
                     fobj.write("{0}\n".format(fname))
 
         logger.info("doing post-install configuration")
-        rb.postinstall(configdir=joinpaths(templatedir,"config_files"))
+        rb.postinstall()
 
         # write .discinfo
         discinfo = DiscInfo(self.product.release, self.arch.basearch)

src/pylorax/treebuilder.py

@@ -80,9 +80,10 @@ class RuntimeBuilder(object):
         '''Install packages and do initial setup with runtime-install.tmpl'''
         self._runner.run("runtime-install.tmpl")
 
-    def postinstall(self, configdir="/usr/share/lorax/config_files"):
+    def postinstall(self):
         '''Do some post-install setup work with runtime-postinstall.tmpl'''
         # copy configdir into runtime root beforehand
+        configdir = joinpaths(self._runner.templatedir,"config_files")
         configdir_path = "tmp/config_files"
         fullpath = joinpaths(self.vars.root, configdir_path)
         if os.path.exists(fullpath):