fix: io_tools/tpcc/Dockerfile to reduce vulnerabilities

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-UBUNTU1604-BASH-542609
- https://snyk.io/vuln/SNYK-UBUNTU1604-GZIP-2442559
- https://snyk.io/vuln/SNYK-UBUNTU1604-LIBGCRYPT20-1585790
- https://snyk.io/vuln/SNYK-UBUNTU1604-SYSTEMD-1320131
- https://snyk.io/vuln/SNYK-UBUNTU1604-TAR-3261141

io_tools/tpcc/Dockerfile

@@ -1,4 +1,4 @@
-FROM ubuntu:16.04
+FROM ubuntu:xenial-20210416
 
 RUN apt-get update && apt-get install -y \
   mysql-client \