Fix Sonar issue: Code readability

Fix Sonar issue: Code readability

Adress Major sonar issues for NeutronHostconfigVppListener.java file.
This patch improves code readability.

Use final temporary var instead of using the method parameter
vhostMode.
Reduce the lambda content by creating a new method:
processDataTreeModification.
Reduce the cyclomatic complexity of validateVppNode by adding the
boolean function isCapabilitiesPresent.

Change-Id: Ie2b3fa85772707f8c86901415dd1ca8d0a7eef47
Signed-off-by: mcauffiez <mcauffiez@inocybe.com>