Error when Running on Docker

- I am trying to run Iperf within a Docker container as specified in
(https://github.com/GoogleCloudPlatform/PerfKitBenchmarker/wiki/Running-on-Docker)
- The command I am using is:
$ ./pkb.py --project= --benchmarks=iperf --os_type=ubuntu_container

- I have Docker installed on my machine (can use "docker run hello-world) but I am getting a error:
**RemoteCommandError: Got non-zero return code (1) executing sudo docker exec None bash -c 'sudo rm -r /var/lib/apt/lists/*'
(which is followed later by)
STDOUT: STDERR: sudo: docker: command not found**

Not sure why I am getting the error. Any ideas? Would appreciate it very much thanks!