Add flag to force namespace isolation

[aledbf]

fixes #597

[k8s-reviewable]

This change is 

[coveralls]

Coverage decreased (-0.07%) to 46.136% when pulling 77c9f4e on aledbf:force-isolation into 03cae88 on kubernetes:master.

[gianrubio]

@aledbf as I understand this PR it to completely isolate the ingress in a namespace. A proof of concept is to enable RBAC in a cluster and deny all "communication" between namespaces.

Following this idea, we should check the namespace of this args:

• publishSvc
• defaultSvc
• configMap
• tcpConfigMapName
• udpConfigMapName

It'll be good to block passing both args watchNamespace and force-namespace-isolation because they conflict.

Another important test is to check if all the annotations are in the same namespace.
ex: ingress.kubernetes.io/auth-tls-secret: default/my-cert