Reducing duplicated values on values files for SiaB

Reduced the amount of duplicated values between seba-ponsim values file.
To deploy, for example, the latest of seba-ponsim, now both seba-ponsim.yaml and seba-pomsim-latest.yaml values files need to be used with the specified order.
Makefile for SiaB is modified accordingly in the patch https://gerrit.opencord.org/#/c/16743/.
Also:
- removed stratumEnabled value from Mininet chart and added mnStratumSwitchCount
- moved bngAppUrl and bngAppVersion values on root of values file

Change-Id: I26b8e91f868646adc06f2c1feea72b333defd487
diff --git a/mininet/templates/deployment.yaml b/mininet/templates/deployment.yaml
index 90d54b2..ba653b7 100644
--- a/mininet/templates/deployment.yaml
+++ b/mininet/templates/deployment.yaml
@@ -40,7 +40,7 @@
         - name: {{ .Chart.Name }}
           image: "{{ .Values.global.registry }}{{ .Values.images.mininet.repository }}:{{ tpl .Values.images.mininet.tag . }}"
           imagePullPolicy: {{ .Values.images.mininet.pullPolicy }}
-{{- if $.Values.stratumEnabled }}
+{{- if gt ($.Values.mnStratumSwitchCount|int) 0 }}
           command: ["python"]
 {{- end }}
           args: [{{ .Values.topoScript }}]