qa/admin/pcp-qa-summary: fix -f arithmetic
qa/admin/pcp-qa-summary: fix -f arithmetic

Failure % should be calculated basewd on the number of hosts with
some QA results, not the number of hosts with some QA failures.

Problem was not visible until we got a significant number of hosts
with 0 failures ... 8^)>

prasincs/pcp,wuliming/pcp,adfernandes/pcp,tjanez/pcp,aeg-aeg/pcpfans,andyvand/cygpcpfans,adfernandes/pcp,adfernandes/pcp,tjanez/pcp,prasincs/pcp,adfernandes/pcp,prasincs/pcp,edwardt/pcp,andyvand/cygpcpfans,mbaldessari/pcp,andyvand/cygpcpfans,andyvand/cygpcpfans,aeg-aeg/pcpfans,mbaldessari/pcp,wuliming/pcp,andyvand/cygpcpfans,adfernandes/pcp,prasincs/pcp,tjanez/pcp,mbaldessari/pcp,edwardt/pcp,adfernandes/pcp,tjanez/pcp,tjanez/pcp,aeg-aeg/pcpfans,andyvand/cygpcpfans,andyvand/cygpcpfans,wuliming/pcp,wuliming/pcp,edwardt/pcp,aeg-aeg/pcpfans,mbaldessari/pcp,tjanez/pcp,edwardt/pcp,adfernandes/pcp,adfernandes/pcp,aeg-aeg/pcpfans,mbaldessari/pcp,tjanez/pcp,wuliming/pcp,aeg-aeg/pcpfans,mbaldessari/pcp,tjanez/pcp,prasincs/pcp,wuliming/pcp,aeg-aeg/pcpfans,wuliming/pcp,aeg-aeg/pcpfans,wuliming/pcp,andyvand/cygpcpfans,edwardt/pcp,edwardt/pcp,edwardt/pcp,prasincs/pcp,prasincs/pcp,prasincs/pcp,edwardt/pcp