ImportError: No module named yaml with run_chroot_local (jenkins-script) fails

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Trying out run_chroot_local, I get the following error (full log):

$ run_chroot_local precise amd64 /home/rospasta/catkinws prerelease groovy openhrp3
  - ubuntu distro:  precise
  - architecture:   amd64
  - script:         prerelease
  - workspace:      /home/rospasta/catkinws
  - script args:    groovy openhrp3
:
vvvvvvvvvvvvvvvvvvv  pbuilder-env.sh vvvvvvvvvvvvvvvvvvvvvv
+ export CCACHE_DIR=/var/cache/pbuilder/ccache
+ CCACHE_DIR=/var/cache/pbuilder/ccache
+ export PATH=/usr/lib/ccache:/home/rospasta/catkinws/devel/bin:/opt/ros/groovy/bin:/usr/lib/lightdm/lightdm:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games
+ PATH=/usr/lib/ccache:/home/rospasta/catkinws/devel/bin:/opt/ros/groovy/bin:/usr/lib/lightdm/lightdm:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games
:
============================================================
+ /home/rospasta/catkinws/jenkins_scripts/prerelease groovy openhrp3
Traceback (most recent call last):
  File "/home/rospasta/catkinws/jenkins_scripts/prerelease", line 2, in <module>
    from test_repositories import *
  File "/home/rospasta/catkinws/jenkins_scripts/test_repositories.py", line 6, in <module>
    import yaml
ImportError: No module named yaml

I first suspected that python's path wasn't set right, but other modules seem to be previously imported without an issue. Looking at this thread I now feel like looking into pbuilder but does anyone already have any idea? Thanks.