Cisco VPN device driver - support IPSec connection updates

Provides simple support for IPSec connection updates, by first marking
the connection as "changed" along with the update notification. Then,
during the sync processing, deleting the connection and then re-creating
it for any changes made.

Added REST client method to allow changing the IPSec connection tunnel
to admin up/down, based on change made to tunnel directly or indirectly
(via service admin state change).

In addition, instead of deleting the IPSec connection, when it is forced
down (due to admin state change for VPN service or IPSec connection),
will send a REST request to the CSR to do a "shut" on the tunnel. When
both the VPN service and IPSec connection are admin up, a REST request
will do a "no shut" on the tunnel.

In the future, can consider revising to a more intelligent scheme, where
we maintain the running state of the connection, and then compare to "sync"
data to determine if a change has occurred. For changes, individual update
REST messages could be made to the tunnel configuration, and then a
shut/no-shut performed to effect the change. For now though, will avoid
that complexity.

Modified UTs for the support of IPSec connection update requests (used to
throw an "unsupported" exception), and to check that the state changing is
processed correctly.

Closes-Bug: 1303830