arm-pods:1,3; dea: Modify interfaces properties: MTU

arm-pods:1,3; dea: Modify interfaces properties: MTU

arm-pod2: check 8826cffe65acf34822a9ed4665267f4de6dc65ca
arm-pod1, arm-pod3, virtual_kvm:
Modify MTU value from null into 9000 for each
interface belonging to each node.
Values are to be merged into each fuel node dictionary
by key reference.

JIRA: https://jira.opnfv.org/browse/ARMBAND-199

Change-Id: Ieb80e51087d756499e0591d972aa8edd2fbabf1a
Signed-off-by: Catalina Focsa <catalina.focsa@enea.com>
(cherry picked from commit b770bb40eb4ffd94133ac83bc1e50be01242ad89)