qa: fix filtering of nginx install test on non-nginx buildbot hosts
qa: fix filtering of nginx install test on non-nginx buildbot hosts

adfernandes/pcp,aeg-aeg/pcpfans,adfernandes/pcp,adfernandes/pcp,edwardt/pcp,edwardt/pcp,edwardt/pcp,edwardt/pcp,edwardt/pcp,edwardt/pcp,adfernandes/pcp,aeg-aeg/pcpfans,wuliming/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,aeg-aeg/pcpfans,aeg-aeg/pcpfans,edwardt/pcp,edwardt/pcp,aeg-aeg/pcpfans,aeg-aeg/pcpfans,aeg-aeg/pcpfans,wuliming/pcp,aeg-aeg/pcpfans,wuliming/pcp,wuliming/pcp,wuliming/pcp,adfernandes/pcp,wuliming/pcp,wuliming/pcp,wuliming/pcp