Don't read/write same file as many times as _replace

[ChangBo Guo(gcb)]

update.py handle base name replacement after copying each file. Current , we read/write same file for each replacement,
We'd better collect the replacements and read/write file only one time for all replacements.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/86221

[Openstack Gerrit (openstack-gerrit)]

Reviewed: https://review.openstack.org/86221
Committed: https://git.openstack.org/cgit/openstack/oslo-incubator/commit/?id=e9ad8a513a19619d425b98cf419dc9a057fb355d
Submitter: Jenkins
Branch: master

commit e9ad8a513a19619d425b98cf419dc9a057fb355d
Author: ChangBo Guo(gcb) <email address hidden>
Date: Wed Apr 9 11:44:12 2014 +0800

    Let update.py read/write same file one time for all replacements

    update.py handles base name replacement after copying each file.
    We read/write same file for each replacement, we'd better collect
    all replacements and read/write file only one time for all replacements.

    Change-Id: Ifa274b6f4426fa0e65e5a3d6fd40dfde3aff1bd2
    Closes-Bug: #1304788