Hey Rohan,
I resolved this issue by adding the following recipe for defusedxml to:
meta-ros/recipes-devtools/python/python-defusedxml_0.4.1.bb
The contents of the recipe is:
DESCRIPTION = "XML bomb protection for Python stdlib modules"
SECTION = "devel/python"
LICENSE = "PSFL"
LIC_FILES_CHKSUM = "file://PKG-INFO;beginline=8;endline=8;md5=a560e172e996ab553d352ccff41c7d20"
SRCNAME = "defusedxml"
SRC_URI = "http://pypi.python.org/packages/source/d/defusedxml/defusedxml-${PV}.tar.gz"
SRC_URI[md5sum] = "230a5eff64f878b392478e30376d673a"
SRC_URI[sha256sum] = "cd551d5a518b745407635bb85116eb813818ecaf182e773c35b36239fc3f2478"
S = "${WORKDIR}/${SRCNAME}-${PV}"
inherit setuptools
Then adding a dependency to roslaunch_1.12.2.bb for this python module.
The following commit is a complete fix.
https://github.com/shadowboxtech/meta-ros/commit/280a89272c24e2a66b2a480f9d2552c81da1e4c9
The resulting image file for the entire Linux OS including roscore is about 47MB in size which is considerably smaller than an Ubuntu image. However, this is for the absolute minimum user tools and ROS install.
Mike