[Schema transformer] Fix error case when object disappear

During SNAT tests where I set and clear router's gateway interface in a
loop (that creates and deletes a virtual network, a service instance, virtual
machines with VMIs, a network policy and a routing table each time), I
get some issues with the schema transformer which tries to access
resources that already gone.
That patch regroups the fixes I should done to not crash the schema
transformer during that tests.

Change-Id: Iebed35eb64e2541e317230b628812db97bd55020
Signed-off-by: Édouard Thuleau <edouard.thuleau@cloudwatt.com>
[SVC monitor] Fix typo in virtualization type

Repalace 'virtulisation' by 'virtualization'

Change-Id: If65652a1420de0f5ce9d6a53752adc9040b3b3ee
Signed-off-by: Édouard Thuleau <edouard.thuleau@cloudwatt.com>
Add vrouter netns script manager

Command line to set up a Linux network namespace between two virtual
networks. And set up all netns configuration to source NAT traffic comes
from left network to the right network. That script could evolves to
manage LBaaS (HAproxy) too.
TODO: if the IP address is not provide, it should start a DHCP client to
obtain the IP configuration.

Change-Id: Ibc169ed1cf569dce1eb094f765e45288c68e2c80
Signed-off-by: Édouard Thuleau <edouard.thuleau@cloudwatt.com>
Delete vrouter reference on VM deletion

For source-nat service instance, virtual machines composed the service
instance have a back ref on a vrouter. Delete the reference on that
vrouter before deleting the virtual machine.

Change-Id: I697583dbf54662b98f50648ec506123424a6c3ab
Signed-off-by: Édouard Thuleau <edouard.thuleau@cloudwatt.com>
[Schema transformer] Retrun a correct set from VirtualNetworkST.delete

The methode VirtualNetworkST shoud always return a set() event if the
virtual network was already deleted.

Change-Id: Ib34bc255c3e63e70ecfa8e8c73f2786c60bd3845
Signed-off-by: Édouard Thuleau <edouard.thuleau@cloudwatt.com>