Move Cisco VPN RESTapi URI strings to constants

Cisco VPN RESTapi URI strings are currently spread out
throughout the cisco vpn device driver code. This create
challenge towards consistently using REST resource identifiers
as this code gets enhanced in the future. This change moves
those URIs as string contents towards the top of the device
driver file.

This addresses the review comment received during the
cisco-vpnaas BP implementation.

Change-Id: I17e02cca95b1d14d9218f1a2745780bd14c9f89d
Closes-Bug: #1313801
Big Switch: Only update hash header on success

This patch moves the hash update call into the success block
of the server manager so the database isn't updated with
a hash header from an error response. Additionally, it prevents
the hash from being updated to an empty value if the hash header
is not present in the response.

Closes-Bug: #1348766
Change-Id: I512d01f9bb91b208dd58883d2464951ecc6748e1
Remove redundant topic from rpc calls

RpcProxy sets by default topic=self.topic, there's no need to specify
it explicitly in derived class, unless it is overridden

Change-Id: I19b9a67072a7f3c42e3b0e4ba412241a056a79a3
Closes-bug: 1348180
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 "Big Switch: Only update hash header on success"
Merge "Remove redundant topic from rpc calls"
Merge "Radware: When a pip is needed, reuse the Port"
Merge "Move Cisco VPN RESTapi URI strings to constants"