code coverage: voip-be-on-merge-request

The JBM coverage is decent, but the voip-be-on-merge-request is not included in the analysis. I suggest to modify ci/ivas_voip_be_test.sh in line with ci/smoke_test.sh, such that one may bypass the build and run with a single thread, and then add this script to the coverage job.

I can take a look at this, but @kiene, @sagnowski, feel free to comment.