Provision chromeos-server-tester{1, 2} was stuck at puppet run


root@chromeos-server-tester2:/usr/local/google/home/nxia# pstree -a -l  159564
sync_and_run_pu /root/chromeos-admin/puppet/sync_and_run_puppet -f
  └─run_puppet puppet/run_puppet
      └─puppet /usr/bin/puppet apply --confdir /root/chromeos-admin//puppet --detailed-exitcodes /root/chromeos-admin//puppet/manifests/site.pp
          ├─sh -c \012      set -eu\012      /usr/local/google/home/chromeos-test/autotest/site_utils/setup_dev_autotest.sh -p autotest -a /usr/local/google/home/chromeos-test/autotest -m -n -v\012      sudo chown root:root /usr/local/autotest/containers/base || true\012      
          │   └─setup_dev_autot /usr/local/google/home/chromeos-test/autotest/site_utils/setup_dev_autotest.sh -p autotest -a /usr/local/google/home/chromeos-test/autotest -m -n -v
          │       └─sudo apt-get install lxc -y
          │           └─apt-get install lxc -y
          │               └─dpkg --force-confold --force-confdef --status-fd 24 --configure libboost-thread1.54.0:amd64 cgroup-lite:all libseccomp2:amd64 lxc-common:amd64 liblxc1:amd64 libpam-cgfs:amd64 librados2:amd64 librbd1:amd64 python-requestbuilder:all bridge-utils:amd64 distro-info-data:all distro-info:amd64 euca2ools:all python3-lxc:amd64 lxc1:amd64 lxc-templates:amd64 lxcfs:amd64 python-distro-info:all qemu-utils:amd64 sharutils:amd64 cloud-image-utils:all debootstrap:all lxc:all
          │                   └─libpam-cgfs.pos /var/lib/dpkg/info/libpam-cgfs.postinst configure 
          │                       └─frontend -w /usr/share/debconf/frontend /usr/sbin/pam-auth-update --package
          │                           ├─pam-auth-update -w /usr/sbin/pam-auth-update --package
          │                           └─whiptail --backtitle Package configuration --title PAM configuration --output-fd 11 --defaultno --yesno -- One or more of the files \012/etc/pam.d/common-{auth,account,password,session} have been locally \012modified.  Please indicate whether these local changes should be \012overridden using the system-provided configuration.  If you decline this\012option, you will need to manage your system's authentication \012configuration by hand.\012\012Override local changes to /etc/pam.d/common-*? 14 77
          └─{puppet}