Virtualbox vm keeps on running after build

Virtualbox vm not stopping after build got over. Here is the status of the vms in my system:

root@dockerhub:~# VBoxManage list vms
"ci-docker1.7.1-virtualbox-centos6.8" {8c6fb17f-7ef3-4145-bec5-0e29d848a9ed}
"ci-docker1.7.1-virtualbox-centos6.8-runner-189d895d-concurrent-0" {c630f4b9-2ec5-4bab-9237-9d04c7dfa7ff}
root@dockerhub:~# VBoxManage list runningvms
"ci-docker1.7.1-virtualbox-centos6.8-runner-189d895d-concurrent-0" {c630f4b9-2ec5-4bab-9237-9d04c7dfa7ff}

Test host system is Debian v8.3 with VirtualBox v5.0.20 and gitlab runner v1.2.0