Polybase with SQL Server 2019 on Linux or Containers
After a lot of trial and error and a lot of research, I found a solution.
I tried both Ubuntu 16.04 and Ubuntu 18.04.  This installation approach works for both, but I only was able to get Polybase to work under Ubuntu 18.04.
I performed a fresh install of Ubuntu and SQL Server.  As with every attempt, everything went well except the installation of the mssql-server-polybase-hadoop package. It failed on attempting to find and install the mssql-zulu-jre-11 package.
However, I downloaded the .deb package and manually installed it from these locations:
Ubuntu 16.04:  https://packages.microsoft.com/ubuntu/16.04/prod/pool/main/m/mssql-zulu-jre-11/mssql-zulu-jre-11_11.43.56-1_amd64.deb
Ubuntu 18.04:  https://packages.microsoft.com/ubuntu/18.04/prod/pool/main/m/mssql-zulu-jre-11/mssql-zulu-jre-11_11.43.56-1_amd64.deb
After installing it with dpkg -i, I was able to then install the mssql-server-polybase-hadoop package.
This process allowed me to configure and use Polybase.  (Only with Ubuntu 18.04)