[Ansible Testbed Setup] Fail on build sonic-mgmt docker

[weijeng]

Description
Follow the README, there is a fail when build sonic-mgmt docker
https://github.com/Azure/sonic-mgmt/blob/master/ansible/doc/README.testbed.Setup.md

Ubuntu version
user@ubuntu-1604:~$ cat /etc/lsb-release
DISTRIB_ID=Ubuntu
DISTRIB_RELEASE=16.04
DISTRIB_CODENAME=xenial
DISTRIB_DESCRIPTION="Ubuntu 16.04.4 LTS"

Steps to reproduce the issue:

1. git clone --recursive https://github.com/Azure/sonic-buildimage.git
2. make configure PLATFORM=generic
3. make target/docker-sonic-mgmt.gz
   Log file: https://www.dropbox.com/s/hwmmegzqji1bdva/docker-sonic-mgmt.gz.log?dl=0

Describe the results you received:
Found existing installation: pycparser 2.14
Cannot uninstall 'pycparser'. It is a distutils installed project and thus we cannot accurately determine which files belong to it which would lead to only a partial uninstall.

Describe the results you expected:

Additional information you deem important:

[qiluo-msft]

Thanks reporting! We are checking.

[weijeng]

Successfully built docker-sonic-mgmt.gz
Thanks a lot~