New install on Mysql Community Server 5.7 - Ubuntu 16.04

You are trying to install PXC over conflicting packages of MySQL Community. This is not going to work this way. You have to first uninstall mysql-community-server and similar packages. Best to backup the datadir before doing so. If you still have problems, check what’s still installed:

dpkg -l|egrep -i "mysql|maria|percona"