Add top level build script for building packages.

ports/python/build.sh

Index: ports/python/build.sh
diff --git a/ports/python/build.sh b/ports/python/build.sh
old mode 100755
new mode 100644
index a4a8d508b784c59aa68131c37ef64f2a6d9c42f3..eb9c36ebf02f4537f454d4498fed36ef66432252
--- a/ports/python/build.sh
+++ b/ports/python/build.sh
@@ -3,8 +3,6 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-source pkg_info
-source ../../build_tools/common.sh
 
 EXECUTABLES=python${NACL_EXEEXT}
 
@@ -55,6 +53,3 @@ TestStep() {
     TranslateAndWriteSelLdrScript ${pexe} x86-64 python.x86-64.nexe python
   fi
 }
-
-PackageInstall
-exit 0