Support enhancements to Cisco CSR VPN REST APIs

Incorporate latest enhancements and fixes in Cisco CSR router REST API
to the VPNaaS device driver and unit test cases. Primarily, is support in
the REST API for different IKE and IPSec encryption algorithms, name length
error handling, disable of anti replay window, and IKE keep alive.

Also includes minor typos and comment fixes mentioned in previous reviews.

Note: notest_cisco_csr_rest.py, which tests the CSR REST client, is not
part of the UT suite yet, pending resolution of httmock package inclusion
as test requirement.

Change-Id: I931f487fbd4ead93a1648e89c9c383b3d55fc07c
Closes-Bug: 1303820
Merge "Support enhancements to Cisco CSR VPN REST APIs"