remove unneeded call to network_api on rebuild_instance

When rebuilding an instance we call the network_api and which results in
calling neutron and updating the info cache. We do not actually need to
do this as we can get the nw_info directly from the instance's info cache.

Change-Id: I2bcc2f15b1e5bb52d972098c7bc3e12f160b6feb
Closes-bug: 1294914
(cherry picked from commit 982850f0e912e1a72e501e456cb2b5ef94124ca6)
Merge "remove unneeded call to network_api on rebuild_instance" into stable/icehouse