pmcd PMDA: avoid segv for pmcd.hostname
pmcd PMDA: avoid segv for pmcd.hostname

Fast path optimization in fetch_hostname() was not setting avp->cp
before returning ==> kaboom in qa/074 everywhere.

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