Extract the terraform-provider-libvirt build into separate pipeline

[dzintars]

I don't need to build libvirt plugin every time.
Instead i could just use Copy Artifacts plugin to copy the binary.
Also i could use

            parallel {
                stage('Build A') {
                    steps {
                            build job: "/project/A/${env.BRANCH}", wait: true
                    }
                }
                stage('Build B') {
                    steps {
                            build job: "/project/B/${env.BRANCH}", wait: true
                    }
                }
            }

To call the Libvirt pipeline if the artifacts are not presented.