the value of retries is error in _allocate_network

the variable 'retries' stands for the times retried by allocate
network ,but it makes a mistake

Change-Id: Ia4c046641619f619f8bf6205f841b3a332d31260
Closes-Bug: #1363326
Merge "the value of retries is error in _allocate_network"
Merge commit 'refs/changes/41/127941/3' of git://gold.eng.hq.xensource.com/git/github/openstack/nova into tmpbranch