Python dependency scanning fails because of unmet dependencies

We are evaluating the Gitlab Ultimate(12.2) for induction into our CI/CD. There is trouble in integrating dependency scanner with our python project. We don't manage the dependency via requirements.txt but for time being we have generated one for running the scans. The pipeline job fails for some libraries like html5lib in the requirements.txt, because of unmet dependencies saying:

 ERROR: Complete output from command /usr/local/bin/python -u -c 'import setuptools, tokenize;__file__='"'"'/tmp/pip-install-_hoj5e5p/lxml/setup.py'"'"';f=getattr(tokenize, '"'"'open'"'"', open)(__file__);code=f.read().replace('"'"'\r\n'"'"', '"'"'\n'"'"');f.close();exec(compile(code, __file__, '"'"'exec'"'"'))' bdist_wheel -d /tmp/pip-wheel-g3n614hr --python-tag cp36:
  ERROR: Building lxml version 4.4.1.
  Building without Cython.
  ERROR: b'/bin/sh: xslt-config: not found\n'
  ** make sure the development packages of libxml2 and libxslt are installed ** 

I believe html5lib need pre-installed libxml2 and libxslt. So is there a way I can install these in the dependencies in gemnasium image after it's downloaded "registry.gitlab.com/gitlab-org/security-products/analyzers/gemnasium-python:2" image ? I assume it will resolve this error.

Please point out if there is a work around for this one.