Radware: When a pip is needed, reuse the Port

When a pip (Proxy IP) is needed by the driver, do not create
a new Neutron Port every time a pip is needed. Reuse the
existing Port.

Change-Id: I769a9d85e217b30a1ea4d09449ff39bf1ab23c5a
Closes-bug: #1349895
Merge "Radware: When a pip is needed, reuse the Port"