Better accounting of current_size in pools.Pool

[zhangchao]

Cinder uses an SSHPool to manager all ssh clients. It rewrites method get() to "check if a connection is active before returning it" in module cinder.utils. The code is consistent with eventlet whose version <= 0.9.16. But since 0.9.17, the method get() has been improved for better accounting of current_size.
http://bazaar.launchpad.net/~soren/eventlet/trunk/revision/1072#tests/pools_test.py

Besides, when we using the method get() in Huawei driver, error occured when deleting mutiple volumes at the same time.
We found the current_size(5) was larger than max_size(4).

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/36793

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/36793
Committed: http://github.com/openstack/cinder/commit/cccf7b92c189bcadf6898019730d84bfd4fe70b6
Submitter: Jenkins
Branch: master

commit cccf7b92c189bcadf6898019730d84bfd4fe70b6
Author: xiaoxi_chen <email address hidden>
Date: Fri Jul 12 16:51:50 2013 +0800

    Refactor SSHPool.get() to use Pool.get()

    In previous code of SSHPool.get(), we pasted the code
    from Pool.get() and check if a connection is active before return
    it.

    However, it's much simpler and cleaner to just call the Pool.get()
    and then check the connection before return. With this,we can free
    ourselves from manually keeping up with code of Pool.get() in
    upstream package eventlet

    As a side effect,this patch fixed bug #1194393 which caused by a
    previous bug in eventlet codes before revision 1072

    fixed bug #1194393
    Change-Id: Ic2bf2fa1ad82cf8669b6c491c955dcab39eb1510