separate openswan special staff from general vpnaas framework

[Hua Zhang]

initial vpnaas effort puts general vpn framework and openswan stuff into a file (device_drivers.ipsec.py) which will cause other vpn driver implementations import this file, thus they will contain a bunch of openswan stuff. so we had better refactor openswan out in to its own files and give some symmetry to these files

[Hua Zhang (zhhuabj)]

refer Carl's comment in the review link https://review.openstack.org/#/c/144391/11/neutron_vpnaas/services/vpn/device_drivers/strongswan_ipsec.py

[Paul Michali (pcm)]

Hua, are you actively working on this issue?

[Paul Michali (pcm)]

Removed assignee, as hasn't been worked on in over six months. Minor cleanup.

[Armando Migliaccio (armando-migliaccio)]

This is an automated cleanup. This bug report has been closed because it
is older than 18 months and there is no open code change to fix this.
After this time it is unlikely that the circumstances which lead to
the observed issue can be reproduced.

If you can reproduce the bug, please:
* reopen the bug report (set to status "New")
* AND add the detailed steps to reproduce the issue (if applicable)
* AND leave a comment "CONFIRMED FOR: <RELEASE_NAME>"
  Only still supported release names are valid (INCUBATOR-JUNO, LIBERTY, MITAKA, NEWTON).
  Valid example: CONFIRMED FOR: INCUBATOR-JUNO