The puppetdb.service unit file for 4.3.0 has changed the way the service is started and stopped. It now executes "puppetdb {start|stop|reload}". The puppetdb is a script which loads it's available commands from /opt/puppetlabs/server/app/puppetdb/cli/app/${command}. Since the ebuild doesn't currently install these, the service can't be started after upgrading 4.2.x->4.3.0. The fix will be to add extra doins lines to the ebuild. I'll raise a PR for this via GitHub shortly, just raising the bug first so I can track it.
Hopefully, https://github.com/gentoo/gentoo/pull/2857 will do the job.
fixed, thanks