consider de(bi|vu)an version

cdist/conf/type/__grafana_dashboard/manifest

@@ -1,20 +1,29 @@
 os=$(cat $__global/explorer/os)
+os_version=$(cat $__global/explorer/os_version)
 
 case $os in
     debian|devuan)
-        __apt_key_uri grafana \
-           --name 'Grafana Release Signing Key' \
-           --uri https://packagecloud.io/gpg.key
+        case $os_version in
+            8*|jessie)
+                __apt_key_uri grafana \
+                   --name 'Grafana Release Signing Key' \
+                   --uri https://packagecloud.io/gpg.key
 
-        require="__apt_key_uri/grafana" __apt_source grafana \
-           --uri https://packagecloud.io/grafana/stable/debian/ \
-           --distribution jessie \
-           --component main
+                require="__apt_key_uri/grafana" __apt_source grafana \
+                   --uri https://packagecloud.io/grafana/stable/debian/ \
+                   --distribution jessie \
+                   --component main
 
-        __package apt-transport-https
+                __package apt-transport-https
 
-        require="__apt_source/grafana __package/apt-transport-https" __package grafana
-        require="__package/grafana" __start_on_boot grafana-server
+                require="__apt_source/grafana __package/apt-transport-https" __package grafana
+                require="__package/grafana" __start_on_boot grafana-server
+            ;;
+            *)
+                echo "Don't know how to install Grafana on $os $os_version. Send us a pull request!"
+                exit 1
+            ;;
+        esac
     ;;
     *)
         echo "Don't know how to install Grafana on $os. Send us a pull request!"