Build pinentry and start kube via a wrapper script that start gpg-agent

gpg-agent used to be shared with the host system, but now that the
socket has moved to /var/run/user/1000/gnupg/ it is no longer.
Starting gpg-agent with a default configuration causes it to pick up
/usr/bin/pinentry which is a hardcoded default pointing to the wrong
place (pinentry-curses).
By explicitly starting gpg-agent we can override that default.