Adds use of CustomCollector in Prometheus exporter

Using a CustomCollector gives more control over the collection
process, which allows handling the removal of metrics when a NS
is deleted. Metrics now have a lifespan of a collection cycle, so
metrics of deleted vdus are now not visible in the exporter.

It also adds MonCollector class, which allows to abstract collection
logic and facilitates testing.

Signed-off-by: Benjamin Diaz <bdiaz@whitestack.com>
Change-Id: Idfdb86c1ee9facd07187e6582954ae4cab32a5b4
diff --git a/docker/scripts/runInstall.sh b/docker/scripts/runInstall.sh
index ccfc2f3..29ab3c6 100755
--- a/docker/scripts/runInstall.sh
+++ b/docker/scripts/runInstall.sh
@@ -23,5 +23,5 @@
 /bin/bash /mon/osm_mon/plugins/vRealiseOps/vROPs_Webservice/install.sh
 python3 /mon/osm_mon/plugins/OpenStack/Aodh/notifier.py &
 python3 /mon/osm_mon/core/message_bus/common_consumer.py &
-osm-mon-exporter
+osm-mon-prometheus-exporter