re-arrange cockpit installer

scripts/subinstallers/cockpit.sh

@@ -4,27 +4,25 @@
 figlet "Mistborn: Installing Cockpit"
 if [ "$DISTRO" == "ubuntu" ]; then
     echo "Ubuntu backports enabled by default"
-    
-    sudo apt-get install -y cockpit
-
-    if [ "$VERSION_ID" == "18.04" ]; then
-        # no longer supported upstream in Ubuntu 20.04
-        sudo apt-get install -y cockpit-docker
-    fi
 
 elif [ "$DISTRO" == "debian" ]; then
     sudo grep -qF "buster-backports" /etc/apt/sources.list.d/backports.list \
     && echo "buster-backports already in sources" \
     || echo 'deb http://deb.debian.org/debian buster-backports main' | sudo tee -a /etc/apt/sources.list.d/backports.list
     
-    sudo apt-get install -y cockpit cockpit-docker
 
 elif [ "$DISTRO" == "raspbian" ]; then
     
     echo "Raspbian repos contain cockpit"
-    sudo apt-get install -y cockpit cockpit-docker
 
 fi
+    
+sudo apt-get install -y cockpit
+
+if $(sudo apt-cache show cockpit-docker > /dev/null 2>&1) ; then
+    # no longer supported upstream in Ubuntu 20.04
+    sudo apt-get install -y cockpit-docker
+fi
 
 sudo cp ./scripts/conf/cockpit.conf /etc/cockpit/cockpit.conf
 sudo systemctl restart cockpit.socket