- Run lcov_to_cobertura with python3 explicitly
- Install missing lcov dependency perl-JSON

This reverts commit 1118d10e.

Dependency actually required was libxerces-c2-dev, which we now build
from source.

Having libxerces-c-dev interferes with linking.

This reverts commit 351dc685.

The story here:
The DOOCS_ttf2xmllib project uses obsoleted functionality from
libxerces-c2-dev. It should be possible to replace this code with
features from libxerces-c-dev. However ttf2xmllib makes use of
BOTH libxerces-c2-dev and libxerces-c-dev. (which I am guessing is
unnessary)

libbxerces-c2-dev is not distributed on Xenial (this was a 14.04
package). On Xenial this package is replaced by libbxerces-c-dev.

libxerces-c2-dev has been backported and made available on desy Xenial
installations through the doocs-pkgs repo.

DOOCS_ttf2xmllib jenkins job needs this package.

dev-doocs-ttf2xmllib has a build dependency on libxerces. Making this
change assuming editing the docker file is the right way to bring this
in. Else this commit needs to be reverted.

No longer works and blocks runnung the Jenkins job