Fix bug in Jenkinsfile

The "create setup file" failed because coverage module was not found.
It is installed in the virtualenv so the command load the venv first now.

Jenkinsfile

@@ -15,7 +15,7 @@ pipeline {
         }
         stage('Create a setup file...') {
             steps {
-                sh '. ~/.profile && make selfex VERBOSE=1 PYTHONPATH=$PWD/src'
+                sh '. ~/.profile && . ./ci_venv/bin/activate && make selfex VERBOSE=1 PYTHONPATH=$PWD/src'
             }
         }
         stage('Test installation...') {