examples: execute bash sessions in script environment

Previously, the sessions contained only explicitly exported variables
and functions.
This was fragile and in part buggy due to lacking exports.

Interactive features like user-defined aliases and functions are still
working as before.

examples/deploy-container.sh

@@ -81,6 +81,6 @@ echo "Bitcoind data dir:"
 sudo ls -al /var/lib/containers/demo-node/var/lib/bitcoind
 
 # Uncomment to start a shell session here
-# export -f c; bash -li
+# . start-bash-session.sh
 
 # Cleanup happens at exit (see above)