Cache pip paks in var

debian-package/evio/DEBIAN/postinst

@@ -3,8 +3,8 @@
 cd /opt/evio
 python3.8 -m venv venv
 source venv/bin/activate
-pip3 --no-cache-dir install wheel
-pip3 --no-cache-dir install psutil slixmpp requests simplejson ryu
+pip3 --cache-dir /var/cache/evio/ install wheel
+pip3 --cache-dir /var/cache/evio/ install eventlet==0.30.2 psutil slixmpp requests simplejson ryu
 deactivate
 systemctl daemon-reload
 systemctl enable evio